INITED STATES 'ARTMENT OF IMMERCE

BLICATION NBS TECHNICAL NOTE 790

MIDAS

Modular Interactive

Data Acquisition System

Description and Specification
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs. THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Nuclear

Sciences 2 — Applied Radiation = — Quantum Electronics s — Electromagnetics 3 — Time

and Frequency 3 — Laboratory Astrophysics 3 — Cryogenics n. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; provides advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard

Reference Materials and the following divisions: Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor

Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and

Government; cooperates with public and private organizations leading to the development of

technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Institute consists of a Center for Building Technology and the following divisions and offices: Engineering and Product Standards — Weights and Measures — Invention and Innovation — Product Evaluation Technology — Electronic Technology — Technical Analysis — Measurement Engineering — Structures, Materials, and Life Safety* — Building Environment * — Technical Evaluation and Application * — Fire Technology.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective

utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center consists of the following offices and divisions: Information Processing Standards — Computer Information — Computer Services —

Systems Development — Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum

accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data — Office of Technical Information and Publications —

Library — Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg. Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

3 Part of the Center for Radiation Research.

3 Located at Boulder. Colorado 80302.

4 Part of the Center for Building Technology.
n m

- MIDAS Modular Interactive

5-753

Data Acquisition System

-4/

Description and Specification

Charles H. Popenoe

Heat Division

Institute for Basic Standards

National Bureau of Standards Washington, D.C. 20234

and

Mack S. Campbell

Compumetrics Division Tri-Com Inc. 12216 Parklawn Drive

Rockville, Maryland 20852

Te-dhn, ccUl ^yt^fA. /^o, "7?0

,.<:;%

*<"»£*U Of *

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued August 1973
National Bureau of Standards Technical Note 790

Nat. Bur. Stand. (U.S.), Tech. Note 790, 49 pages (Aug. 1973) CODEN: NBTNAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 03.46:790). Price SO. 75
Contents

Page

1. Introduction 1

1.1 Purpose of this Document 3

2. Basic Features and Terminology of the MIDAS System h

3. Operating Configurations and Upgradahility 6

3.1 Stand-alone System - Teletypewriter Control 6

3.2 Stand-alone System - Programming Module Control

with Teletypewriter Output 7

3.3 Computer-Controlled System - Remote TimeShared Computer 8

3.^ Minicomputer Controlled System - Serial

Communication at Normal Data Rate 9

3-5 Minicomputer Controlled System - Serial

Communication at High Data Rate . 10

3.6 Minicomputer Controlled System - Parallel

Communication 11

h. Mechanical Characteristics 12

5. Dataway and Bus Assignments 13

6. System Controller 1^-

6.1 Dataway Terminations l^t

6.2 System Initialization and Reset lU

6.3 Slot Addresses lk

6.U Code Conversion lU

6.5 Strobes 1^

6.6 Synchronization l6

6.7 Inhibit 16

lia
Page

7. Command Structure 16

7.1 USASCII-7 Command Set 16

7.2 System Commands 17

7.3 Module Commands 18

8. System Signals and Timing 18

8.1 Dataway System Lines 18

8.2 General Signal Standards 20

a. Voltage Levels of Dataway Signals 20

b. Rise and Fall Times 20

c. Loading 21

(1) Address Lines (ADDR) 21

(2) All Other Dataway Lines 21

d. Drive Capability 21

9. Power Supplies 21

10. References 22

List of Tables

1. MIDAS Connector Pin Assignments — Normal slot viewed

from front of crate 23

2. MIDAS Connector Pin Assignments — Controller slot

viewed from front of crate 2k

List of Figures

1. MIDAS System consisting of a crate, power supply and a number of single- and double-width modules' vi

2. Simplest Stand-alone MIDAS System 6

3. Stand-alone MIDAS System controlled by Programmer

or Computer Module 7

iv
Page

h. MIDAS System Controlled by Remote Time-shared Computer ... 8

5. MIDAS System Controlled by Local Minicomputer 10

6. MIDAS System Operated Serially through High-Speed

Interface 11

7. MIDAS System Operated from Parallel Computer I/O

Interface 12

8. MIDAS System — Functional Block Diagram 15

APPEM)IX 25
y

Figure 1. MIDAS System consisting of a crate, power supply and a number of single- and double-width modules. The system

controller occupies the rightmost slot position.

VI
MIDAS

Modular Interactive Data Acquisition System

Description and Specification

Charles H. Popenoe and Mack S. Campbell*

The task of interfacing experiments to computers

and data-logging systems should he made as painless as possible for the scientist. With this intent, MIDAS,

a user-oriented, modular digital interface system "based on CAMAC hardware and USASCII-hus data communication

has been developed. MIDAS modules enable the experimenter to set up, program, modify and operate automated

or computer-controlled experiments independently of the

experts. Salient features of the concept are described

and operating configurations discussed both with and

without computer control. System interface requirements

are specified in sufficient detail to enable one skilled

in the art to design and construct modules operable within a MIDAS system.

Key words: Computer-controlled experiment; computer

interfacing; data acquisition system; digital interface;

instrumentation; laboratory automation; MIDAS; programmable controller.

1. Introduction

Historically, laboratory automation has followed two patterns —

either a hard-wired dedicated system has been designed to accomplish a specific function efficiently, or a digital computer has been interfaced to laboratory instruments and then laboriously programmed in

assembly language to perform somewhat more flexibly one or a number of

jobs. The first approach unquestionably leads to an efficient but very

inflexible system which performs the specified task well. However,

requirements in research laboratories continually change, which sometimes leads to scrapping very expensive systems that will no longer

satisfy current needs. The computer approach on the other hand, is a marvelous one for a well-financed, well-staffed establishment with the

necessary expertise in minicomputer programming and digital interfacing

techniques. Lacking this expertise, the experimenter is forced to

either divert time from his research functions to gain education in

these fields or alternatively, to employ the services of experts who

will supply him with the system that he thinks he wants at the time of

*Compumetrics Division, Tri-Com, Inc., 12216 Parklawn Drive, Rockville,

Maryland 20852.
specification. The latter leads to a situation where the experimenter

does not really understand the system and is therefore not capable of

making small changes without again bringing in the experts • Neither of

these approaches supplies the user with what he really needs — a readyto-run universal interface to computers and instruments from any manufacturer which he may plug together quickly himself as easily as he

might plug probes and plug-ins into his familiar oscilloscope; and which

he may then program, run, modify and reprogram on the spot until his

experiment is running to his complete satisfaction.

The decreasing cost and size of integrated circuit logic has

recently made possible data acquisition and control systems which may

operate independently of a computer, yet have many of the attributes of

computer-based systems. These relatively new "programmable" systems are generally modular in concept and programmable by "software" techniques,

employing easily changed program storage such as paper tape, magnetic

tape or punched cards. Such systems must necessarily sacrifice some of

the extreme flexibility and high speed attainable with a machine-language

programmed computer in exchange for simplicity of operation and ease of

programming. This exchange is effected by increasing the complexity of

hardware logic to assume functions once accomplished by sophisticated

computer programming. Hardware costs have, however, been shown to be

small or insignificant when compared to the labor involved in "bringingup" a complex system. We can well afford to spend a few extra dollars

on logic hardware if by doing so we may save a few minutes of an inexperienced user's time in programming or using the resulting system.

We have developed a new system with the acronym MIDAS, which we believe will alleviate many of the present experiment-automation difficulties. MIDAS is a user-oriented, modular, programmable digital interface system based on CAMAC hardware and on USASCII-bus communication

between modules. It has been designed with the idea of making the task

of interfacing instruments , experiments , computers and data-recording

devices as painless as possible for the scientist-user.

The MIDAS concept is based on two strong beliefs. The first is

that a good universal automation system should have enough capability

to handle perhaps 80% of experimental situations without reliance upon

a computer. Computers should properly be reserved for functions that

computers do best — high-speed computation and decision-making. To use

a computer for data acquisition and sequential control is "over-kill".

When these computer attributes are required, however, the same system

which has been running stand-alone must be able to be quickly plugged

into and indeed be controlled completely by a computer, whether it be a local minicomputer or a remotely accessed time-shared facility. It is

important that the systems be upgradable in a rational manner through a series of easy transitions ranging from the simplest stand-alone data

recording system up through a full parallel multi-instrument complex

operating at computer speeds.
The second strong belief underpinning MIDAS philosophy is that some- body must be able to configure and modify conveniently both hardware and

software of every automation system. It is most efficient that this

person be the experimenter himself (noting the exception of very large

systems) provided that he can do so conveniently without having to learn

disciplines such as assembly language computer programming or digital

electronics, which are most probably unrelated to his specialty.

We do not wish to imply that MIDAS can or should be applied to all

situations — it provides no advantage to very large, very small or very

fast experiments. MIDAS was designed to apply to situations requiring

moderate capabilities, where less than state-of-the-art performance is

acceptable, but where cost, setup time and versatility are of great

importance.

In short, MIDAS is meant to be a convenient do-it-yourself automation tool for the experimental scientist. In this respect MIDAS follows

in the tradition established by the creators of OMNITAB* — that perhaps

the best way to help a large number of people with a large need is to

make it very easy for them to help themselves.

1.1 Purpose of this Document

This report is intended to accomplish three purposes. First of

all, it serves to provide an intorduction to the overall philosophy and

functional characteristics of the MIDAS concept. By reading only

Sections 1 through k, an interested person may learn enough about the

salient features of MIDAS and how MIDAS is applied to determine whether

or not the MIDAS approach would be preferable to some other digital

interface standard, such as CAMAC, in the light of his particular requirements and capabilities. Second, this report serves to document and

specify the architecture, organization and electrical and mechanical

standards of the MIDAS system, thus placing these standards and design

concepts in the public domain. We have intentionally attempted to avoid

unnecessary overspecification which would tend to lock the design of

MIDAS components to a particular detail design or logic family. Third,

the report is intended to provide sufficient detailed information to

allow anyone skilled in the techniques of digital logic design to design

and construct modules and controllers which will operate in MIDAS systems

together with components designed by others. The information necessary

to ensure this compatibility is found in the latter half of the document — Sections 5 through 9 including the Tables and Appendix.

*NBS Handbook 101, "OMNITAB, A Computer Program for Statistical and

Numerical Analysis", J. Hilsenrath, G. G. Ziegler, C. G. Messina,

P. J. Walsh and R. J. Herbold.
2. Basic Features and Terminology* of the MIDAS System

(a) MIDAS is a user-oriented digital interface system for

laboratory data acquisition and experiment control,

based on a "buil ding-block or "modular" construction.

It is composed of a number of unit functional "modules"

which may be plugged into "slots" in a standard "crate"

which provides power and interconnections between

modules to create more powerful and complex equipment

assemblies. Each module is in itself a complete independent functional unit, and when plugged into the

crate is able to communicate bidirectionally with other

modules plugged into the same crate or other interconnected crates. A crate, and a number of such intercommunicating modules together with a "program source"

for issuing "commands" to the modules and possibly a "recording device" for recording data and results form

a complete "system".

(b) MIDAS is physically and mechanically based on CAMAC

hardware and dimensions [l] 1

. MIDAS and CAMAC hard- ware and crates are physically interchangeable but are not necessarily electrically compatible, due to differences in operating philosophy.

(c) Individual modules make connection to a standard CAMAC

"dataway" through 86-way connectors mounted at the rear

of the crate. The dataway provides common bussing of

digital data, commands, control signals and power to

the modules

.

(d) MIDAS is a "programmable" system. A module will become

"active" or perform a function in response to a command

present on the dataway. A logical sequence of commands

forms a "program" . All commands and data are transferred between modules in standard 7-bit parallel

USASCII code format [2]. A module may issue commands

to or receive data from any other module, or any device

external to the system which communicates in USASCII

code.

(e) The rightmost two slots in the crate are unique and are occupied by the "System Controller". The System

*In the interest of clarity, MIDAS terminology is enclosed in quotation

marks when first introduced.

^Figures in brackets indicate the literature references at the end of

this paper.
Controller performs in-crate housekeeping functions

decoding system commands and slot "addresses", activating slot positions and generating timing and control

signals. In addition, the System Controller serves as an interface "between MIDAS modules and external recording devices and program sources, performing serialparallel and parallel-serial conversions where necessary.

(f) MIDAS is intended to be used extensively without requirement for an external computer as a "stand-alone" data

acquisition and control system. In its simplest con- figuration, a low-cost teletypewriter ("TTY") serves as

"both program source and recording device. The TTY keyboard and paper tape reader are used to issue commands

to the system, while data is recorded permanently on the

teleprinter and paper tape punch. Hence, the Basic

System Controller interfaces directly with a 20 ma

current-loop TTY operating serially in the full-duplex

mode. Similarly, it will interface directly to a CRT

terminal, or when computer control is desired, will

interface to minicomputers and telephone couplers (timeshared computers) which are TTY-compatible.

(g) There is no inherent limitation to the operating speed

of the MIDAS system other than the limitation imposed

by backplane transmission characteristics. The modules

will operate at the speed of the program source, which

may range from 10 characters (commands) per second for

the slowest serial teletypewriters up to data rates

approaching one megahertz for bit-parallel commands

issued by a minicomputer. Recorded data must naturally

be transferred at the operating rate of the recording

device. It is the function of the System Controller to

synchronize transfer of data and commands between the

MIDAS modules and an external program source or recording

device.

(h) MIDAS is not intended to compete with or supplant CAMAC;

rather, it was developed to fill a void existing between

NIM and CAMAC not serviced by either concept. MIDAS is

for digital data acquisition and control situations of

moderate complexity, where cost, flexibility and ease of programming are paramount, and where computer control

is only an option. It is intended to be used as a general-purpose laboratory instrument to perform many

and varied tasks during its lifetime.

5
3. Operating Configurations and Upgradability

Although MIDAS has been optimized for self-contained "stand-alone"

applications where computer control is not required, the system may he

upgraded through a series of easy transitions to more complex closedloop operation under control of a local or remote computer. In most

cases the transition involves only plugging in an appropriate cable,

and at most, a different module. Several examples of possible operating

configuration follow:

3.1 Stand-alone System - Teletypewriter Control

The simplest MIDAS configuration consists of only a crate with

necessary modules connected through a Basic System Controller to an unmodified teletypewriter through the standard serial data current-loop

connection, with the teletypewriter wired for 20 ma full-duplex operation (fig. 2). This mode of operation employs the teletypewriter keyboard, paper tape reader and answer-back drum for programming the system,

and the teletypewriter printer and tape punch are used for recording the

data in a format controlled by the program. Operating rate of the system

is, of course, limited and determined by the rate of the teletypewriter,

generally 10-30 characters (commands) per second. This rate is sufficient for a surprising number of experimental situations, especially

those involving appreciable settling times such as are encountered in

photometry or calorimetry, or involving very precise measurements which

normally require a period of the order of one second to digitize the

analog signal.

RECORD

TAPE LOOP PROGRAM ANSWER-BACK SUBPROGRAM

TELETYPE

PRINTED/

PUNCH

MIDAS

SYSTEM

READER/

KEYBOARD

> STIMULI

MEASUREMENTS

RECORDERS

Figure 2. Simplest Stand-alone MIDAS System
The program command sequence is punched into paper tape from the

keyboard with the teletypewriter in the LOCAL mode. The program tape is

then loaded into the tape reader and, if the program is repetitive, may

be formed into a continuous loop. Control may be transferred from the

main program in the tape reader to a subprogram coded into the answer- back drum, or the program may halt and request input from the keyboard,

but it is a requirement of this simplest configuration that the program

must be sequential.

3.2 Stand-alone System - Programming Module Control with Teletypewriter Output

The second level of sophistication reached by a stand-alone system

eliminates the teletypewriter tape reader and answer-back drum as the

program source, employing instead a special "Programming Module" to store

the program and issue commands to the system (fig. 3). The teletypewriter is now used solely for entering manual commands and recording the

output data during an experiment. This greatly eases wear on electromechanical components of the teletypewriter and frees the system from

the limitation of running at teletypewriter speeds , except when output

is required. The Programming Module is loaded by entering a command

sequence from the teletypewriter keyboard or reader. This program is

stored in a small memory and may be run by transferring control to the

Programming Module by keyboard or tape command. The program stored in

the memory of the Programming Module need not be entirely sequential,

but may consist of a main program and a number of subprograms which may

be accessed by a "jump" command. Some closed-loop operation may be

incorporated into the program, such as conditional jumps to subroutines

dependent on the state of input lines from the experiment. This form of

operation simulates closely a computer-controlled system except for the

lack of computational capability.

RECORD

COMMANDS TO SXSTEM

STIMULI

MEASUREMENTS

Figure 3. Stand-alone MIDAS System controlled by

Programmer or Computer Module.
More sophisticated Programming Modules may be designed to further narrow the distinction between stand-alone and computer-controlled MIDAS

configurations . There is no reason why Programming Modules should not

have decimal computation capability with conditional jumps dependent on arithmetical or logical comparisons. A MIDAS system operating at this

level approximates a special-purpose computer, with the program potential

limited only by the imagination of the module designer and experiment

programmer. The major disadvantage of this configuration is that programming of computational code is bound to be somewhat onerous due to

limitations imposed by the simplicity of such a "computing module" when

compared to a true computer. Since all computation must be "microprogrammed" in machine code, it would presumably be limited to simple tasks

such as summing, averaging, scaling or arithmetical comparisons.

3.3 Computer-Controlled System - Remote Time-Shared Computer

When the decision has been made to go to computer control, it may be

obtained via the nearest telephone. Figure k illustrates schematically

this form of operation. Notice that the MIDAS system is interposed

between the telephone coupler and the remote terminal, and once again,

the operating speed of the system is determined by the teletypewriter

(or other) terminal.

RECORD <_

SUBPROGRAMS

TELETYPE

PRINTER/

PUNCH

READER/ KEYBOARD

MIDAS

SYSTEM

-> STIMULI — MEASUREMENTS

-*+ RECORDERS

Figure k. MIDAS System Controlled by Remote Time-shared Compute
There are a number of major advantages inherent in this configuration.

First, the extra investment required is quite small when computer control

is only occasionally required — the system is operated as a stand-alone

(sec. 3.1) configuration the majority of the time. Second, this configuration is quite portable and may he used in turn to control several

experiments either stand-alone or under computer supervision. Sharing the

system would he more difficult if the computer and associated peripherals

would have to he moved along with the MIDAS hardware. Third, it allows

great programming simplicity, since it is now possible to program both

commands to MIDAS and sophisticated computations in an easy-to-use,

higher-level language such as BASIC or interactive FORTRAN. These languages are universally available and are already familiar to a large

segment of the research community. Fourth, the experimenter may also

take advantage of all of the benefits of a large computer — program

storage, large data file storage, editing facilities, adequate user core, and possibly high-speed input/output peripherals.

The disadvantages encountered in using a remote time-shared computer

for control are minimal; continuous operation over long periods can run

up sizeable computer bills, and one is, of course, limited to the operating speed of the terminal and timesharing system, although some systems

can operate at several different data transmission rates. There is an additional uncertainty inherent in the response time of a timesharing

system — when heavily loaded, the computer may take several seconds to

respond to output from MIDAS. If operating speed is critical, this con- figuration may seem intolerably slow under peak load conditions.

3.^ Minicomputer Controlled System - Serial Communication at Normal Data Rate

The MIDAS equipment may be plugged in directly into the teletypewriter port of a minicomputer with no additional interfacing, as minicomputers almost invariably have provision for teletypewriter input/

output on a 20 ma current loop interface. Once again the MIDAS system

is simply placed in between the computer and the teletypewriter, as shown

schematically in figure 5. The operating speed is determined by the

teletypewriter speed, generally 10 characters per second. However, the

system may now be operated fully closed-loop and programmed in a higherlevel language such as BASIC. BASIC is available on a number of minicomputers and will run short programs with only h K words of core memory.

The advantages offered by operating in this configuration include rapid

and interactive program generation, debugging' and modification, with

provision for considerable amounts of computation. A MIDAS system

operating through the TTY port functions as a universal interface from

any minicomputer to almost any instrument, facilitating expansion or modification of the system or program to suit the changing requirements

of the experimenter.
RECORD

SUBPROGRAMS

TELETYPE

PRINTER/

PUNCH

READER/ KEYBOARD

LABORATORY MINICOMPUTER OR CALCULATOR

I/O

MIDAS SYSTEM

STIMULI

MEASUREMEHTS

RECORDERS

Figure 5- MIDAS System Controlled by Local Minicomputer.

3.5 Minicomputer Controlled System - Serial Communication at High Data Rate

If higher operating speeds are required, the MIDAS system may "be plugged into a second teletypewriter interface with the teletypewriter

plugged into the customary TTY interface (fig. 6). The clock rate of

the second interface may be adjusted to run at any desired rate up to

at least 9^00 baud. Data and commands are still transmitted by serial

start-stop codes, but in this configuration operation proceeds at nearly

100 times normal teletypewriter speeds . The teletypewriter is used to

communicate with the computer program, which may again be written in

BASIC or equivalent. It is necessary to modify the BASIC system program

slightly to provide for additional commands which address the second

teletypewriter interface as an additional peripheral device of the com- puter having an independent device number. In this way, communication

with the teletypewriter may occur at teletypewriter rate while MIDAS may

communicate with the same BASIC program at a much higher rate. After

reduction of the data brought in through MIDAS, the results may be

printed on the teleprinter at low speeds

.

10
COMMANDS

TO CPU

COMPUTER

BASIC PROGRAM

TELETYPE

SERIAL I/O

HIGH RATE

SERIAL I/O i.

/^

TELETYPE

PRINTER/ PUNCH

'

MIDAS

SYSTEM

READER/ KEYBOARD

>• STIMULI

MEASUREMENTS

5te RECORDERS

Figure 6. MIDAS System Operated Serially through

High-Speed Interface..

3.6 Minicomputer Controlled System - Parallel Communication

The ultimate speed of operation may be realized "by employing parallel data and command transfer between the computer and the MIDAS system.

The Basic System Controller is designed primarily for serial communication; therefore a Parallel System Controller is required to interface

with the minicomputers parallel I/O bus. This controller may be con- siderably less complex than the Basic System Controller due to the

reduced need for timing and serial-to-parallel conversion functions. A

system operating in this configuration is shown in figure 7 which enables

MIDAS to be operated at computer speeds. The penalty paid for parallel

operation lies in the increased difficulty in programming the system, as parallel data transfer must be programmed in machine or assembly language,

It is possible with BASIC interpreters offered by several minicomputer

manufacturers to write machine-language subprograms that may be called

from a BASIC main program to transmit commands to MIDAS or to input data

into the computer through the MIDAS system. Using this technique, com- plex calculations could still be performed entirely in BASIC, but

commands to MIDAS would take the form of CALL subroutines using the

USASCII command as the calling parameter.

11
RECORD «<rCOMMANDS TO CPU

COMPUTER

BASIC PROGRAM TELETYPE

SERIAL I/O

TELETYPE

PRINTER/ PUNCH

READER/ KEYBOARD

JT

PARALLEL I/O INTERFACE uMIDAS

SYSTEM

STIMULI

MEASUREMENTS ^ RECORDERS

Figure 7- MIDAS System Operated from Parallel

Computer I/O Interface.

One possible implementation of this configuration would employ a single universal Parallel System Controller and a number of separate

interface cards designed to interface to specific computers. The

alternative is to have an individual Parallel System Controller designed

to interface directly by cable and plug to the I/O bus of each desired

specific minicomputer family.

h. Mechanical Characteristics

The mechanical characteristics and dimensions of the modules and

crate are entirely according to CAMAC specifications [l]. Excerpts

from this document containing descriptions and details of the CAMAC

mechanical specification are reproduced here in the Appendix; therefore

the discussion of this section will be concise. MIDAS modules are con- structed in CAMAC "plug-in unit" hardware — there is no physical difference between these units and indeed, MIDAS modules could be operated

in a CAMAC system with the proper programming. In addition, MIDAS

systems may be operated in standard CAMAC crates. Standard CAMAC crates,

however, have provision for 25 slots or "stations", somewhat more than

may be addressed by a MIDAS system, which is limited to 16 slots. It is

economically expeditious to construct special crates for MIDAS to CAMAC

specifications, but with 16 instead of 25 slots, effecting some savings

12
in cost. The crate pictured in figure 1 has l6 slots, eight of which are single-width, and 8 of which are double-width. The remaining slot position (No. 25), has a special connector to which a plug-in Power Supplymakes connection when plugged into the crate. This particular power

supply has quintuple-width dimensions, and when inserted into position,

renders 2 double-width slots inaccessible. These slots may be recovered

if necessary by mounting the unit outboard of the crate and making

connections by cable.

5. Dataway and Bus Assignments

The dataway consists of a number of conductors interconnecting the

modules with each other and with the control module. Each slot position

is terminated with an 86-pin etched-circuit type connector [l] which

mates to the etched-circuit extension at the rear of each module. The

connectors are supported and interconnected by means of the "backplane",

which may be either of etched circuit construction or wire-wrap construction, or a combination of the two. The backplane consists of the dataway.

connectors and optional patch pins. All digital communication occurs along "bus-lines" connecting corresponding pins together at all slot

positions along the dataway.

Two slot positions at the extreme right-hand side of the crate are reserved for the use of the System Controller. The rightmost slot is

unique, having connections to all individual slot positions, but not

having access to the data bus-lines. The second slot position from the

right is normal in all respects but as with CAMAC, is reserved for the

use of the controller. The remaining ik slot positions are available for

us e by any module

Additional bus-lines bring power to all slot positions, and provide

power-return and "clean ground" bussing throughout the crate. There are five uncommitted contacts at each slot position. Two of these are "free

bus-lines" and are connected across all normal slot positions. The

remaining three are "patch-points" and may be employed arbitrarily to

establish nonstandard interconnections at the user's option.

So far, the backplane and dataway layout have followed the CAMAC

specification exactly. The use of the various bus-lines and MIDAS

signal assignments do not necessarily follow the CAMAC usage; however,

for comparison, CAMAC pin assignments may be found in the Appendix and

reference 1. MIDAS pin assignments are detailed in table 1 for "normal"

module slots, and in table 2 for the Controller position. It is seen

that although many of the functions are identical, differences in operating philosophy preclude a one-to-one correspondence between the two

systems

13
6. System Controller

While the individual modules provide interfacing between external

instruments or devices to be monitored and controlled and the MIDAS

system, the System Controller provides the interface between programming

and recording devices and the system, and is necessary for directing

communication between modules . It may indeed be considered to be the nerve center of the system, being the only module having access to all

lines and busses on the backplane. The architecture of the MIDAS system

may best be understood by reference to figure 8, in which the general

functions of the System Controller are schematically outlined. Specific

minimum functional requirements of the System Controller are described

below.

6.1 Dataway Terminations

All dataway busses are "wired-or" logic driven by open collector

drivers in the modules. The System Controller must terminate all busses

with approximately 3 k ohms to +5 V.

6.2 System Initialization and Reset

The System Controller is responsible for generating a bus signal

upon initial application of power to the system. This initialization

may also optionally be generated by system command or manual switch

closure.

6.3 Slot Addresses

Slot addresses are decoded by the controller corresponding to the

system commands A through 0. These are used to activate the proper line

to the addressed module, enabling it to respond to succeeding commands

on the Command bus. System Commands to accomplish simultaneous addressing of two or more modules must be decoded and interpreted by the con- troller.

6.U Code Conversion

All commands placed onto the command bus and data received from the

data bus are in 7-bit parallel ASCII code. The controller must perform

any conversions necessary to interface with external programming and

recording devices which use other codes. Similarly, serial-to-parallel

and parallel-to-serial conversions are performed in the controller when

required to interface with serial input/output devices.

6.5 Strobes

The controller must generate strobes for each command directed to

modules. These strobes are to be generated only when the logic lines

have settled sufficiently to produce a valid command character and

correct parity is established.

lit
CO

CO

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15
6.6 Synchronization

The controller must synchronize all data and command transfer

between system modules and programming/recording devices. Transfer must

be in full-duplex mode since there is no general limitation on simultaneous transmission and reception by the modules. A signal is generated

by the controller to inform any module wishing to transmit data that the

controller is busy and cannot receive. This signal may be used to synchronize the transfer of strings of characters from the modules. When a module has finished its transmission of a string of data, it generates

another signal to inform the controller of this condition.

If it is required that the programming device be temporarily halted

to allow completion of a module operation before resumption of the

program command sequence, the controller must recognize system commands

to enable the "waiting" function, and must respond to a completion signal

from the module to restart the programming device.

The controller must clear the command bus and relinquish control

over the system when a signal from an alternate programming device is

present. It will, however, continue to transmit data to the recording

device as dictated by the data strobe.

6.7 Inhibit

An additional responsibility of the controller is to generate an "inhibit" bus signal which inhibits sequencing of the programming device

and halts all in-progress operations in the modules. A front panel

connector must be available to allow a signal to be brought in from the

outside world to inhibit system operation.

7. Command Structure

7.1 USASCII-7 Command Set

There are 256 possible code combinations formable using all eight

bits of the USASCII-8 code, X3.U-I967 [2]. Unfortunately, the complete

USASCII-8 code set is able to be utilized on only a very few types of

equipment. Additionally, there are obvious advantages to using the

eighth bit of an 8-bit code to provide a capability to check parity.

Such practical considerations lead to the limitation of the valid code

combinations for MIDAS to the lower-order 7 bits, the widely-used

USASCII-7 code, consisting of 128 possible characters. The only character which is inherently unusable as a MIDAS command character is the

rubout character "DEL" (octal 177), since it must be blocked from the

system to allow correction of program tapes and to provide a code

signifying "no-operation".

Of the USASCII-7 code, 32 characters (octal 000 through 037) represent control functions and are therefore non-printing. The lower-case

font (octal lUO-176) is unusable on many devices including less-expensive

16
teletypewriters . These characters are all potentially usable as commands

to MIDAS equipment, and as such are not excluded from the possible

command set. It is strongly recommended, however, that only the printing

characters (octal 1+0 through 137) be used as program commands, since

programs composed of this set may be listed on the teletypewriter for

program verification and debugging.

7.2 System Commands

Of the printing character set, 32 characters are reserved for MIDAS

system commands and are interpreted by the System Controller. The

reserved set includes the punctuation marks from octal 1+0 through 57 and

the characters octal 100 through 117. The latter group includes the

alphabetical letters A through which designate the slot addresses.

The use of the remaining system commands is arbitrary and is left to the

discretion of the controller designer. The reserved System Commands and

their octal representations are listed below:

Octal Character Octal Character

1+0 Space 100 e

1+1 ; 101 A

U2 ii 102 B

1+3 # 103 C

1+1+ $ 10 1+ D

^5 % 105 E

1+6 & 106 F

U7 i 107 G

50 ( 110 H 51 ) 111 I

52 * 112 J

53 + 113 K

51+ 5 111+ L

55 - 115 M

56 . 116 N

57 / 117

17
7.3 Module Commands

The remaining 96 characters not reserved above are usable by module

designers as commands to modules, subject to the previous recommendation

that only printing characters be selected when possible.

8. System Signals and Timing

8.1 Dataway System Lines

A number of dataway lines are reserved for system-required functions.

The application, requirements and timing of these signals are discussed

in the following sections. In all cases the dataway busses use "wiredor" logic; therefore all bus signals present on the dataway are negative-true (3.5-5 volts = logical "0"; 0-.5 volts = logical "l").

(a) CMMD (COMMAND MODE) is generated by the System Controller and

indicates to all modules that the system is in the "COMMAND" mode — that

all character codes present on the Command bus are to be interpreted as commands. The CMMD signal additionally indicates that the Data bus is

not being used by the controller and is therefore free to be used by the

modules

(b) CONTB (CONTROLLER BUSY) is generated by the System Controller

at any time when the Controller is unable to respond to a data strobe

(DATAS) generated by a module. It is present during the time required

for the controller to transmit a character to, say, the teleprinter. The

trailing edge of CONTB indicates that the controller is ready to accept

a new data character from a module.

(c) ALT CONT (ALTERNATE CONTROLLER) is generated by a module

desiring to take over system control. It disables the normal System

Controller, and prevents it from responding to MODD signals. Upon

receipt of this signal, the System Controller clears the Command bus

and relinquishes control to the module generating the signal, after

which the alternate controlling module may place characters on the

Command bus

(d) IDSC (INHIBIT DATASTROBE TO CONTROLLER) is generated by a module when communicating data between modules. IDSC prevents the

System Controller from responding to DATAS. Thus, a module would generate this signal whenever it wished to place data on the Data bus which

was not intended for an action by the System Controller such as output

of that character on the teleprinter.

(e) DATAS (DATA STROBE) is generated by a module when data on the

Data bus is valid and may be transferred. Lines of the Data bus must be

stable for at least 100 ns prior to the leading edge of DATAS. Pulse

width may vary with system operating rate but must not be shorter than

1 ps nor longer than strobe S2.

18
(f) MODB (MODULE BUSY) is generated by a module in response to

addressing that module with ADDR, to indicate that the addressed module

is still busy performing an operation initiated by a previous command

and is therefore incapable of receiving new commands.

(g) MOLD (MODULE DONE) is a pulse generated by a module upon com- pletion of a module operation. It may be used to restart system operations following a pause initiated by a WAIT command. The pulse width

must lie between 1 and 10 ys , and the leading edge of MODD must be

delayed at least 1 ys after the leading edge of strobe SI.

(h) M0DE0T (MODULE END-OF-TRANSMISSION) is generated by a module

having the capability of transmitting a variable-length string of data

characters in response to a single command. After all characters in the

data string have been transmitted, the module activates the M0DE0T bus

to notify the controller that the transmission is complete. The con- troller uses this information to synchronize and interlock communications

with the programming device, recording devices, and/or remote lines.

(i) INH (INHIBIT) may be generated by modules, System Controller or devices external to the system. It is normally used to provide a failsafe interlock capability in standalone systems, and interrupts all

activity if a limit in the external experiment has been exceeded. The

INH line going low causes action to both System Controller and modules.

The System Controller must be inhibited from placing further commands on the Command bus, and the programming device interrupted. All modules

having an operation in process as a result of previous commands must

cease activity until the condition causing actuation of the INH line has

been corrected.

(j) SI (STROBE l) indicates that data on the Command bus is valid

and may be transferred. Lines comprising the Command bus must be stable

for at least 100 ns prior to the leading edge of SI. The width of SI may

vary with operating rate but must not be shorter than 1 ys.

(k) S2 (STROBE 2) is identical to SI except for timing. S2 immediately follows SI, having its leading edge coincident with the trailing

edge of SI. The command bus lines must remain stable for a minimum of

100 ns following the trailing edge of S2. This strobe may be "turned

around" by a module to strobe data onto the Data bus

{I) ADDR (SLOT ADDRESS) is generated by the System Controller only.

There is one ADDR line from the System Controller to each slot position.

The ADDR signal is used to activate a module in the addressed slot position. There is no limitation to the number of slots which may be

addressed simultaneously. The MODB line will go low in response to ADDR

if an operation is in process in the addressed module. Modules have no

access to ADDR lines other than their own, and most therefore go through

the System Controller to address another module.

19
(m) LAM ( LOOK-AT-ME ) lines are counterparts to the ADDR lines but

transfer signals in the opposite direction — from modules to the System

Controller. There is a LAM line from each slot position leading only to

the controller slot position. A signal generated by a module placed on this line notifies the controller that the module requires attention.

The LAM lines may thus be used as an interrupt network, giving capability

to a MIDAS system run by an intelligent program source to jump to an interrupt routine to service the module requesting attention.

(n) INIT (INITIALIZE) will be present at system startup or system

reset and must set all control registers and bistable elements to a defined state. It is generated by the System Controller.

(o) CI - Cl8 (COMMAND BUS) consists of eighteen lines used to

transfer commands from the System Controller to the modules. The least

significant seven bits (Cl-CT) are normally used as the MIDAS USACII-T

Command bus . The total number may be used during parallel command

operations when used with a minicomputer.

(p) Dl - Dl8 (DATA BUS) consists of another eighteen lines

reserved for transfer of data words from the modules. Again only lines

D1-D7 are used for transferring USASCII-T data characters. The full

complement may be used for parallel data transfer to a minicomputer.

(q) 60 HZ (60 HERTZ CLOCK) is an ac line frequency 5-volt square wave generated by the System Controller and available on this bus-line

for use by the modules for timing purposes.

(r) EARTH (ANALOG RETURN) is an isolated "clean" ground bus

intended to be used by analog circuitry as the return line. This bus

must be kept free from digital switching transients. It may be left

isolated or tied to digital ground or earth ground at one point as required.

8.2 General Signal Standards

a. Voltage Levels of Dataway Signals

All dataway signals must conform to the following:

"0" State "1" State

Accepted at input +2.0 to +5-5 v to +0.8 v

Generated at output +3.5 to +5.5 v to +0.5 v

Rise and Fall Times

Rise and fall times of dataway signals shall not be faster than

U0 ns to keep cross-coupling among dataway lines to a reasonable level.

20
c. Loading

!l) Address Lines (ADDR)

Maximum signal requirement:

0.1+ ma at "o" state

(2) All Other Dataway Lines

Maximum signal requirement:

1+0 pa at "0" state

1.6 ma at "l" state.

d. Drive Capability

Dataway drivers shall be open- collect or type capable of sinking at least 25 ma at 0.1+ v maximum.

9 . Power Supplies

Module designers may assume that three power supplies are available

in a MIDAS crate. These are a +6 Vdc supply capable of supplying 10 or more amperes of well-regulated and filtered power for digital logic

circuitry, and a positive and negative 12 Vdc supply for analog circuitry,

The additional mandatory CAMAC supplies (-6 Vdc and ±2U Vdc) may be

supplied if required for the particular installation or if it is planned

to operate both CAMAC and MIDAS modules in the same crate, but are not

specified or required for MIDAS systems.

It is optional whether the power supplies are mounted at the rear

of the crate or constructed in modular plug-in form and inserted from the

front of the crate as is done in the system shown in figure 1.

The minimum power supply specifications are outlined below

Logic Supply

+6 Vdc ±1%

10 amp @1+5°C

105-120 Vac, 60 Hz

0.25% line and load

less than 10 mv p-p

6.5 V crowbar

Voltage:

Current Output

Input

Regulation:

Ripple

Overvoltage:

Analog Supplies

±12 Vdc ±1%

1 amp each @1+5°C

105-120 Vac, 60 Hz

0.25% line and load

less than 10 mv p-p

21
10 . References

[l] "CAMAC: A Modular Instrumentation System for Data Handling;

Revised Description and Specification", USAEC TID-25875,

(July 1972).

[2] Little, John L. , "Some Evolving Conventions and Standards for

Character Information Coded in Six, Seven, and Eight Bits",

Nat. Bur. Stand. (U.S.) Tech. Note U78, (May 1969).

22
TABLE I

MIDAS CONNECTOR PIN ASSIGNMENTS - NORMAL SLOT VIEWED FROM FRONT OF CRATE ALL DATAWAY SIGNALS ARE NEGATIVE-TRUE

CAMAC DESIGNATION

MIDAS MIDAS

DES IGNATION

PI* - P2*

PIN NO. DESIGNATION

PATCH 1 PI Alt >+3> B BUS 1 P2 U5 U2 Fl6

PATCH

POINTS

P3

pl+ P5

P3

Pit P5

^6

1+7

1+8

1+1

1+0 39

F8

Fl+ F2 X kg 38 Fl

INH* I 50 37 A8

C 51 36 AU ADDR N 52 35 A2 LAM L 53 3^ Al

STROBES

SI*

L S2*

SI

S2

51* 55 33

32 %

Q

INIT* MODB*

CONTB* W2U 56 31 W23 IDSC* ALT CONT* W22 57 30 W21

CMMD* W20 58 29 W19

- Cl8* Wl8 59 28 W17 C17* -| Cl6* Wl6 60 27 W15 C15*

/"I /"\H n X ft T\TT"\ ClU* wiU 61 26 W13 C13* COMMAND C12* W12 62 25 Wll Cll* BUS CIO* WIO 63 21+ W9 C9*

C8* W8 61+ 23 W7 C7* C6* w6 65 22 W5 C5*

Ck* wit 66 21 W3 C3*

C2* W2 67 20 Wl CI* -J MODD* R2U 68 19 R23 DATAS*

R22 69 18 R21 MODEOT*

R20 70 17 R19

" D18* R18 71 16 R17 D17* - Dl6* Rl6 72 15 R15 D15*

DlU* Rll+ 73 lit R13 D13*

D12* R12 7U 13 Rll Dll* DATA DIO* RIO 75 12 R9 D9* BUS D8* R8 76 11 R7 DT* D6* r6 77 10 R5 D5*

DU* B.k 78 9 R3 D3*

D2* R2 79 8 Rl Dl* -1 r -12V* -12 80 7 -21+ +200 81 6 -6 POWER 60HZ*

ACL

Yl

8283

5

1+ ACN

E EARTH*

BUS +12V* +12 8k 3 +21+ Y2 85 2 +6 +6v*

- GND* 86 V

GND* J

COMMAND

BUS

DATA

BUS

POWER

BUS

*BUS-LINE SIGNALS

23
TABLE II

MIDAS CONNECTOR PIN ASSIGNMENTS - CONTROLLER SLOT VIEWED FROM FRONT OF CRATE ALL DATAWAY SIGNALS ARE NEGATIVE-TRUE

CAMAC

MIDAS

DESIGNATION

DESIGNATION

MIDAS

PIN NO. DESIGNATICIN

r

P1 PI /hh H5n B PATCH

POINT

P2

P3

pit

P2

P3

Pit

1+5 U2

1+6 1+1

1+7 1+0

Fl6

F8

Fl+ L P5 P5 1+8 39 F2

X 1+9 38 Fl

INH* I 50 37 A8

C 51 36 Al+ PATCH f P6 POINTS L P7 P6 52 35 A2

P7 53 3U Al

SI* SI 5!+ 33 Z IN IT*

S2* S2 55 32 Q MODB*

L2U 56 31 N2l+ L23 57 30 N23

L22 58 29 N22

L21 59 28 N21

L20 60 27 N20

L19 61 26 N19

Ll8 62 25 N18

L17 63 21+ N17

Ll6 61+ 23 N16

L15 65 22 N15 - LlU 66 21 Nll+ -> N L13 67 20 N13 N M L12 68 19 N12 M

L Lll 69 18 Nil L K LIO 70 17 N10 K

J L9 71 16 N9 J SLOT LOOK-AT-ME I L8 72 15 N8 I ADDRESS

LINES H L7 73 ll+ N7 H LINES

(LAM) G L6 lh 13 N6 G (ADDR)

F L5 75 12 N5 F E hk 76 11 Nl+ E

D L3 77 10 N3 D

C L2 78 9 N2 C - B LI 79 8 Nl B -1 r

-12V* -12 +200

ACL

80 7 81 6 82 5-21+ -6ACN

—

60HZ* Yl 83 1+ E EARTH*

POWER +12V* +12 81+ 3 +2l+ POWER

BUS Y2 85 2 +6 +6v* BUS

- GND* 86 l GND* -

v> y

* BUS-LINE SIGNALS

2U
APPENDIX excerpted from TID-25875

To be used in conjunction

with TID-25877

INSTRUMENTATION CATEGORY UC-37

CAMAC

A MODULAR INSTRUMENTATION SYSTEM

for DATA HANDLING

Revised Description and Specification

Endorsed by

AEC NIM Committee

(AEC Committee on Nuclear Instrument Modules) ABSTRACT

CAMAC is a digital data handling system in widespread use with on-line digital processors and computers. The

system is based on a digital highway for data and control. Mechanical and signal standards are specified to ensure

physical and operational compatibility between units from different sources. Except for pages i-vi, 46A and 46B,

this report is identical to EURATOM Report EUR 4100e dated 1972. AEC Report TID-25877 constitutes a supplement to and is to be used in conjunction with this report. This revised specification introduces several new

features but is consistent with the previous version (EUR 4100e, 1969).

The CAMAC system was specified by European laboratories through the ESONE Committee and has been endorsed by the U.S. AEC NIM Committee.

KEY WORDS

CAMAC

COMPUTER INTERFACING CONTROL SYSTEMS

INSTRUMENTATION

INSTRUMENTATION STANDARDS

NUCLEAR INSTRUMENTATION

STANDARDS

REFERENCE AEC REPORTS

TID-25876 Branch Highway

TID-25877 Supplement

Edited for the NIM COMMITTEE

by Louis Costrell, NIM Committee Chairman

National Bureau of Standards

25
3. BASIC FEATURES OF THE CAMAC SYSTEM

This specification is intended to serve as a basis for a range of modular instrumentation capable of

linking transducers and other devices with digital controllers or computers. It consists of mechanical

standards and signal standards that are sufficient to ensure compatibility between units from

different sources of design and production.

The basic features of CAMAC are summarised as follows:

(a) It is a modular system, with functional units which can be combined to form equipment

assemblies.

(b) The functional units are constructed as 'plug-in units' and are mounted in a standard 'crate'. (c) The mechanical structure is designed to exploit the high component packing density possible with integrated circuit packages and similar devices. (d) Each plug-in unit makes direct connection to a standard 'Dataway'. This highway forms part of

the crate and conveys digital data, control signals and power. The standards of the Dataway

are independent of the type of plug-in unit or computer used.

(e) The system has been designed so that an assembly consisting of a crate and plug-in units can be connected to an on-line digital computer. However, the use of a computer is entirely optional and no part of this specification depends upon its presence in the system.

(f) External connections to plug-in units may conform to the digital or analogue signal standards of associated transducers, computers etc., or to the recommended standards given in this speci- fication (for digital signals) and EUR 5 1 OOe (for analogue signals). (g) Assemblies of up to seven CAMAC crates may be interconnected by the CAMAC Branch Highway specified in EUR 4600e.

(h) No licence or other permission is needed in order to use this specification.

4. MECHANICAL CHARACTERISTICS

CAMAC is a modular system. Equipment assemblies are formed by mounting appropriate plug-in

units in a standard chassis or crate. Each plug-in unit occupies one or more mounting stations in the

crate. At each station there is an 86-way connector socket giving access to the CAMAC Dataway, a data highway which forms part of the crate. The Dataway consists mainly of bus-lines for data, control and power.

Drawings for the manufacture of CAMAC compatible crates and plug-in units can be derived from

the definitive dimensions given in Figures 1-3 for crates, Figure 4 for plug-in units, and Figure 5 for Dataway connector plugs and sockets.

Recommended dimensions for ventilated crates, NIM adaptors, and printed wiring cards for plug-in

units are given in the non-mandatory Figures 6-8, respectively.

All dimensions in these Figures are in millimetres unless indicated otherwise.

4.1 The Crate The crate mounts in a 1 9-inch rack and has up to 25 stations for plug-in units on a pitch of

l 7- 2mm. Each station has upper and lower guides for the runners of a plug-in unit, an 86-way

Dataway connector socket, and a tapped hole for the fixing screw of a plug-in unit. Modules

conforming to the USAEC NIM specification (see Appendix 2) can be mounted in the crate on

their basic pitch of 34-4mm (see Section 4.3).

Unless indicated otherwise, all crates must conform to Figures 1-3 and those parts of

Figure 5 defining the connector socket.

26
Sections 4. 1 . 1 . and 4. 1 . 2 are comments on these Figures.

4.1.1 Dimensions

Figure 1 shows the front view of a basic 25-station crate which occupies the minimum

height of 5U (U = 44-45mm). Crates may have less than 25 stations, which, as indicated by Note 3 on Figure 1 , need not be positioned symmetrically.

The lower cross-member has holes tapped ISO.M4 pitch 07 for the fixing screws of CAMAC plug-in units, and intermediate holes tapped UNC 6-32 for the lower fixing screws of NIM units. The upper cross-memoer may also have holes for the fixing screws of NIM units. The positions of these holes for CAMAC and NIM units, relative to the left- hand edge of the front aperture, are given in Figure 1 by the formulae for dimensions 'z' and 'w', respectively.

The positions of the centres of the guides, also relative to the left-hand edge of the

aperture, are given by the formula for dimension 'x' in Figure 1 . Detail A shows the entry

into a guide. The dimensions of the 'lead-in' are not specified.

Detail B gives dimensions provisionally specified for 19-inch rack-mounting equipment by

the International Electrotechnical Commission in their document IEC 45 (Central Office) 24.

Figure 2 is a plan view of the lower guides in the crate. In order to remove any heat generated in the plug-in units it is necessary to provide adequate ventilation through the bottom and top of the crate. The unobstructed area between adjacent guides, both at the top and bottom of the crate, is not permitted to be less than 1 5cm2 and should preferably be distributed over the full depth of the crate from the front cross-members to the Data- way assembly. If crates such as that shown in Figure 1 (with height 5U) are mounted

above or below other equipment (including other similar crates) it may be necessary to use intermediate deflectors, etc., to ensure adequate ventilation. Alternatively, the crate may be extended to include additional ventilation features, as described in Section 4.1.3.

Figure 3 is a sectioned side view on the offset line d-d in Figure 1 , passing through the

centre of an upper guide and a ventilating space between lower guides. The front faces of

the upper and lower cross-members constitute the vertical datum of the crate. This datum

is set back from the front face of the crate by a distance 'e', typically between 3 and 4mm,

so that the front panels of plug-in units do not project beyond the front of the crate. The

backs of the crate-mounting flanges are typically, but not necessarily, aligned with the datum.

The front ends of the upper and lower guides may be set back from the vertical datum. The guides extend sufficiently far towards the rear of the crate to ensure that the connector plug of a plug-in unit is guided into the entry of the connector socket.

The minimum overall depth of the crate provides mechanical protection for the Dataway

assembly. The side panels are shorter than the frontal height of the crate (see dimensions

'a' in Figures 1 , 3 and 6) to permit the use of typical runners for supporting the crate in the rack. This reduction in height extends at least to within 25mm of the rear face of the rack-mounting flanges of the crate.

The running-surface of the lower guide constitutes the crate horizontal datum. The Data- way assembly is not permitted to extend upwards more than 135mm from this horizontal datum, so that there is unrestricted access to the upper part of the rear of plug-in units.

27
The positions of the connector sockets are defined with respect to the three datum lines of the crate. The centre lines of the sockets are defined with respect to the left-hand edge

of the front aperture by dimension 'y' in Figure 1 . The vertical datum of the sockets is shown relative to the vertical datum of the crate in Figures 2 and 3, and the horizontal datum of the sockets relative to the horizontal datum ot the crate in Figure 3.

4.1.2 Dataway Connector Sockets The Dataway connector sockets have two rows of 43 contacts on a pitch of CM inch

(2 - 54mm). Mandatory and recommended dimensions of the sockets are given in Figure 5, together with additional 'commonly used' dimensions upon which the designs of many

existing crates and Dataway assemblies have been based.

The vertical datum of the connector sockets is the nominal position of the leading edge of

the connector plug of a plug-in unit fully inserted into the crate. The position of the

vertical datum is defined in Figure 5.5 with respect to other functional features of the

socket. In some commonly used sockets the plane of the mounting face coincides with

the vertical datum of the connector socket, but this is not necessarily so.

The maximum forward projection of the connector socket in front of the vertical datum

is shown in Figure 5.5. The shapes of the straight or curved chamfers that guide the connector plug into the socket are shown in Figures 5.6, 5.7 and 5.8. Within the minimum

width shown for each chamfer the angle between any tangent to the chamfer and the line of entry of the connector plug does not exceed 60°.

If the front aperture of the crate extends to the inner surface of the right-hand side panel

(as in Figures l and 2) the adjacent connector socket cannot exceed the recommended

width of I2mm. Elsewhere, sockets up to the maximum width of l7-2mm can be used.

The dimensions of the contacts of the connector socket are shown in Figure 5.4. The

position of each edge is defined by a dimension (d, D) relative to the horizontal datum of

the socket, and is completely independent of the positions of all other edges on both rows

of contacts.

Alternatively, a connector socket with point contacts may be used, in which case the

distance between each point contact and the horizontal datum of the connector socket is (2-56 + 2-54k) ±0-13.

4.1.3 Optional Features of the Crate The height of the crate may be extended by an integral number of U units (U = 44-45mm),

as in Figure 6, in order to provide an entry for cool air, which then flows up between the

guides, and an exit for any warm air that may be rising from equipment below.

A crate may have fewer than 25 stations. The width of the front aperture is 17- 2s-oomm

for s stations, and formulae given in Figure 1 are used for locating the guides, connector

socket, etc. at each station.

Power supply units may be mounted at the rear of a CAMAC crate. The overall depth of a crate with rear-mounted power supplies may be limited by the depth of the rack. A

recommended maximum depth of 525mm is shown in Figure 3. A power supply unit is not allowed to extend upwards above the maximum height of the Dataway assembly. It should not obstruct the entry or exit of the ventilating air flows in a crate such as that shown in Figure 6. The width of a rear-mounted power supply is limited to 447mm.

28
4.2 Plug-in Units

Basically a plug-in unit consists of a front panel with fixing screw, top and bottom runners that

slide in the guides of the crate, and an 86-way Dataway connector plug. The connector plug is typically an integral part of a printed-wiring card, but may be a separate male connector mounted at the rear of the plug-in unit. A plug-in unit may occupy more than one station and,

if so, may have more than one set of runners and more than one connector plug.

Unless indicated otherwise, all plug-in units must conform to Figure 4 and those parts of

Figure 5 defining the connector plug.

The following sections are comments on these Figures.

4.2.1 Dimensions The horizontal datum of a plug-in unit is the edge of the lower runner. The vertical datum

is the rear face of the front panel. The upper and lower parts of the rear face should be in contact with the cross-members of the crate when the plug-in unit is fully inserted. Figure 4 therefore requires that the upper and lower 1 1 mm of the rear face of the front panel

are free from projections, other than the fixing screws.

Figure 4 shows the dimensions of single-width and double-width plug-in units and gives general formulae for the front-panel widths of units.

It is recommended that the fixing screw should also provide a jacking action to assist in overcoming the insertion and withdrawal forces of the connector socket. The fixing screw

of a single-width plug-in unit is located on the centre line of the front panel. If a multiple- width unit has only one fixing screw, and this has a jacking action, the screw should be

positioned to give the most effective pull and thrust against the insertion and withdrawal

forces of the Dataway connector or connectors (hence it should be at the same station as

a single connector or approximately symmetrical with respect to two or more connectors).

Above the maximum height of the Dataway assembly there can be projections at the rear of the plug-in unit, extending more than 290mm from the vertical datum. Below this height, in order to provide clearance for the connector socket, only the connector plug is allowed to extend beyond 290mm.

There should be adequate ventilation through the bottom and top of each plug-in unit to remove any heat generated within the unit.

4.2.2 Dataway Connector Plug The dimensions of the connector plug are shown in Figures 5.1, 5.2 and 5.3.

The full 86 contacts are always present and extend to the extreme edge of the plug, without

a chamfer, in order to avoid the risk of damage to the contact plating of connector sockets by exposed abrasives in the substrate of the connector plug.

Chamfers are provided at the top and bottom of the connector socket and are therefore not needed at the top and bottom corners of the connector plug where the maximum

permitted chamfer is 1 x 1 mm. For at least 1 3mm from the edge of the plug the contacts

are straight and plated.

29
The dimensions of the contacts of the connector plug are shown in Figure 5.3. The

position of each edge is defined by a dimension (h, H) relative to the horizontal datum

and is completely independent of the position of all other edges on both sides of the plug. The lowest contact on each side of the plug may be extended to the horizontal datum in order to reduce the impedance of the OV line.

4.2.3 Insertion of the Plug-in Unit into the Crate

In the initial stages of insertion the plug-in unit is supported by the lower guide in the

crate. The upper runner, although within the guide, has some vertical clearance. When the

plug-in unit is fully inserted the connector plug is located by the connector socket and the

front panel is supported by the securing screw. The top and bottom runners are then

within the guides and approximately parallel to them, but both have some vertical clearance. The transition between these two states is described in detail below.

The dimensions of the guides and runners (Figures 1 and 4) ensure that the plug-in unit moves freely and is guided so that the leading edge of the connector plug enters the chamfers of the connector socket. The lower corner of the leading edge of the plug comes

into contact with the chamfer at the bottom of the connector socket. Further insertion of

the plug-in unit lifts the connector plug until its lower edge rests on the horizontal datum

face of the connector socket. Even a connector plug with the maximum permitted

1 x 1mm chamfer will have been lifted into correct alignment before any electrical contact occurs between the connector plug and socket. The position of maximum

insertion without electrical contact, even with a maximum thickness plug, is defined in Figure 5.5 with respect to the vertical datum of the connector socket.

Before this point has been reached it will have been possible to engage the fixing screw in the corresponding tapped hole in the lower cross-member of the crate. This can be

facilitated bv having a tapered end to the screw, so that the front panel is lifted into the

correct alignment. The fixing screw has a jacking action which can be used to draw the

plug-in unit further into the crate.

Further insertion of the plug-in unit brings the contacts of the plug and socket into engagement, and the insertion force of the connector is encountered. The recommended

maximum insertion and withdrawal forces are 80 Newtons for each connector plug. Forces in excess of this can cause difficulty in inserting and withdrawing the plug-in unit and can also result in damage to front panels, etc.

Figure 5.5 defines, with respect to the vertical datum of the connector socket, the line beyond which there is reliable contact between corresponding contacts on the plug and

socket, even with a plug of minimum thickness.

Finally, when the plug-in unit is fully inserted in the crate, the leading edge of the connector plug is nominally at the vertical datum of the connector socket and the lower datum face of the front panel of the plug-in unit is in contact with the lower cross- member of the crate. However, the forces due to the connector socket and jacking screw

are not in line and tend to lift the connector plug off the horizontal datum of the socket,

in which case there may be clearance between the upper datum face of the front panel and the upper cross member. Figure 5.5 ensures that there is adequate clearance beyond

the extreme position of the connector plug, by defining a minimum distance between the

vertical datum of the socket and any internal obstruction.

30
4.2.4 Printed-Wiring Card

Figure 8 gives recommended dimensions for a printed-wiring card suitable for use with

typical (but not necessarily all) commercially available frameworks for plug-in units con- forming to this specification.

4.2.5 Other Connectors Connectors or other components such as switches may be mounted on the front panel, or

at the rear of the plug-in unit above the maximum height limit of the Dataway assembly.

For coaxial connectors the LEMO 00C50 (50J2 impedance) connector or an equivalent type is strongly recommended.

There may, however, be special circumstances requiring the use of other connectors in order to suit a specific external equipment with which the plug-in unit is closely

associated.

4.3 Adaptor for NIM Units

Plug-in units conforming to the USAEC NIM Specification (see Appendix 2) can be inserted into the guides of a CAMAC crate. In order to supply power to a NIM unit, which is shorter than a CAMAC plug-in unit, an adaptor is required between the Dataway connector socket and

the connector on the NIM unit. The essential dimensions of such an adaptor are given in Figure 7.

4.4 The Dataway

Communication between plug-in units takes place through the Dataway. This passive multi-wire highway is incorporated in the crate and links the Dataway connector sockets at all stations. The Dataway consists of signal lines and power lines, as shown in Table I.

The extreme right-hand station, as viewed from the front of the crate, has the special role of

control station. The data lines in the Dataway are accessible at the remaining normal stations, but not at the control station.

Most signal lines are bus-lines linking corresponding contacts of the Dataway connector sockets

at all normal stations and, in some cases, the control station. There are also individual lines, each linking one contact at a normal station to one contact at the control station. At each

station there are contacts for unspecified uses. Two of these contacts are linked across all normal stations to form free bus-lines. The remainder are available as patch contacts, but do

not have specified Dataway wiring. The Dataway construction may extend these patch

contacts, and others associated with the individual lines and certain bus-lines, to more readily accessible patch points to which patch connections can be attached.

The power lines link corresponding contacts of the Dataway connector sockets at all stations. The power return line (OV) links two contacts in parallel at all stations.

31
TABLE I STANDARD DATAWAY USAGE

TITLE DESIGNATION CONTACTS USE AT A MODULE

Command

Station Number

Sub-Address

Function

N

A1,2, 4, 8 F1,2,4, 8, 16

14

5

Selects the module (1 ndividual line from control station). Selects a section of the module.

Defines the function to be performed in the module.

Timing

Strobe 1 Strobe 2

S1S2

1

1

Controls first phase of operation (Dataway signals must not change). Controls second phase (Dataway signals may change).

Data

Write Read W1-W24

R1-R24

2424Bring information to the module. Take information from the module.

Status Look-at-Me Busy

Response Command Accepted

LBQ

X

1

1

1

1

Indicates request for service (Individual line to control station). Indicates that a Dataway operation is in progress. Indicates status of feature selected by command.

Indicates that module is able to perform action required by the command.

Common Controls

Initialise Inhibit ClearZ

IC

1

1

1

Operate on all features connected to them, no command required. Sets module to a defined state. (Accompanied by S2 and B). Disables features for duration of signal. Clears registers. (Accompanied by S2 and B).

Non-Standard Connections

Free bus-lines Patch contacts

P1.P2 P3-P5

2

3

For unspecified uses. For unspecified interconnections. No Dataway Lines.

Mandatory Power Lines +24V d.c. +6V d.c. -6V d.c. -24V d.c. OV

+24

+6

-6-24

1

1

1

12

The crate is mired for mandatory and additional lines.

Power return.

Additional Power Lines +200V d.c. + 12V d.c. -12V d.c. 117V a.c. (Live) 117V a.c. (Neutral) Clean Earth Reserved

+200

+12

-12 ACL ACN

E Y1.Y2

1

1

1

1

1

12

Lines are reserved for the following power supplies Low current for indicators etc.

Reference for circuits requiring clean earth. Reserved for future allocation.

TOTAL 86

32
TABLE II CONTACT ALLOCATION AT A NORMAL STATION

(Viewed from front of crate)

Bus-line Bus-line

Individual patch contact

Individual patch contact

Individual patch contact

Bus-line

Bus-line

Bus-line

Individual line Individual line Bus-line

Bus-line

Free Bus-line Free Bus-line

Command Accepted

Inhibit Clear

Station Number

Look-at-Me

Strobe 1 Strobe 2

24 Write Bus-lines

W1 = least significant bit W24 = most significant bit

24 Read Bus-lines

R1 = least significant bit R24 = most significant bit

Power

Bus-lines

-12V d.c. +200V d.c.

1 17V a.c. Live Reserved +12V d.c. Reserved OV (Power Return)

P1P2

P3

P4P5X

ICN

L

S'1 S2W24

W22

W20

W18 W16

W14

W12

W10 W8

W6W4

W2

R24 R22

R20 R18 R16

R14

R12

R10

R8R6

R4

R2

-12

+200 ACL

Y1

+12 Y2

B Busy F16 Function F8 Function F4 Function F2 Function

F1 Function A8 Sub-address A4 Sub-address A2 Sub-address A1 Sub-address Z Initialise Q Response W23

W21 W19

W17 W15

W13

W11 W9

W7W5

W3

W1

R23

R21 R19

R17

R15 R13

R11 R9

R7R5

R3

R1-24 -24V d.c. -6 -6V d.c. ACN 117V a.c. Neutral

E Clean Earth +24 +24V d.c. +6 +6V d.c. 0V (Power Return

Bus-line Bus-line

Bus-line

Bus-line

Bus-line

Bus-line

Bus-line

Bus-line Bus-line

Bus-line

Bus-line

Bus-line

Power

Bus-lines

The assignment of contacts at the Dataway connector and their connections to bus-lines, individual lines and patch contacts must be as shown in Table 11 for normal stations and

Table 111 for the control station. The control station must be to the right of all normal

stations.

33
TABLE III CONTACT ALLOCATION AT THE CONTROL STATION

(Viewed from front of crateI

Individual patch contact

Individual patch contact

Individual patch contact

Individual patch contact

Individual patch contact

Bus-line Bus-line

Bus-line

Individual patch contact

Individual patch contact

Bus-line

Bus-line

Command Accepted

Inhibit Clear

Strobe 1 Strobe 2

24 individual Look-at-Me lines L1 from Station 1, etc.

Power

Bus-lines

-12Vd.c. +200V d.c. 117V a.c. Live Reserved +12Vd.c.

Reserved OV (Power Return)

P1P2P3

P4P5X

IC

P6

P7

SIS2L24

L23

L22

L21 L20

L19 L18

L17

L16

L15 L14

L13

L12

L11 L10

L9L8

L7

L6L5

L4

L3

L2

L1-12 +200 ACL

Y1

+ 12 Y2

B Busy Bus-line F16 Function Bus-line F8 Function Bus-line F4 Function Bus-line F2 Function Bus-line F1 Function Bus-line A8 Sub-address Bus-line A4 Sub-address Bus-line A2 Sub-address Bus-line A1 Sub-address Bus-line Z Initialise Bus-line Q Response Bus-line N24 ~ N23

N22

N21 N20

N19

N18

N17 N16

N15

N14

N13 24 individual Station Number lines N12 N1 to Station 1, etc. N11 N10 N9

N8

N7N6N5

N4

N3

N2

N1-24 -24V d.c. -6 -6V d.c. ACN 117V a.c. Neutral Power

E Clean Earth > Bus-lines +24 +24V d.c. +6 +6Vd.c. 0V (Power Return)

The method of construction of the Dataway must be consistent with the signal standards

for signal lines (see Section 7) and with the maximum current loads specified for the power lines (see Section 8).

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1*2

S. GOVERNMENT PRINTING OFFICE
form NBS-114A (1-71) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-790

2. Gov't Accessio No.3. Recipient's Accession No.

4. TITLE AND SUBTITLE MIDAS Modular Interactive Data Acquisition System - Description and Specification5. Publication Date August 1973

6. Performing Organization Code

7. AUTHOR(S)

Charles H. Popenoe and Mack S. Campbell

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. Project/Task/Work Unit No. NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Same as No . 9

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.)

The task of interfacing experiments to computers and data-logging systems

should be made as painless as possible for the scientist. With this intent, MIDAS,

a user-oriented, modular digital interface system based on CAMAC hardware and

USASCII-bus data communication has been developed. MIDAS modules enable the experimenter to set up, program, modify and operate automated or computer-controlled

experiments independently of the experts. Salient features of the concept are described and operating configurations discussed both with and without computer

control. System interface requirements are specified in sufficient detail to enable one skilled in the art to design and construct modules operable within a MIDAS system.

17. KEY WORDS (Alphabetical order, separated by semicolons) Computer-controlled experiment; computer interfacing; data acquisition system; digital

interface; instrumentation; laboratory automation; MIDAS; programmable controller.

18. AVAILABILITY STATEMENT m UNLIMITED.

I I FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

h9

22. Price

75 cents

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