A VME-base Data-Acquisition System for Scattering Experiments
At a Pulsed Neutron Source.
S.Satoh and M.Furusaka, KEK, Tsukuba, Japan

Abstract
We developed a VME-base data-acquisition system forscattering experiments at a pulsed-neutron source. Singleended and linear-position sensitive 3He neutron detectors
are used in various neutron-scattering experiments. The
data are acquired by multi-channel time analyzer (TA)and position-sensitive detector (PSD) modules on a VME
system.
We use a PC in place of a VME CPU module, which isusually necessary to use the VME system. For thispurpose, we developed an interface-module (SCSI-VME)
which performs read/write data from/to VME modules via
a standard SCSI connection. By employing the SCSI
standard, we can use any PCs or workstations. A VMEbase data-acquisition system with a PC is shown in Fig. 1.
The PC controls three daisy-chained VME crates by SCSIcables.

Figure2: The SCSI-VME module•••••••

Compact size: It is housed in a VME double-height
1-span module.
Transfer speed: The net speed is about 0.5µsec/byte.
PC: Any PCs or workstations which have a SCSIport.
A GPIB port: It has a GPIB port. (Always acts as acontroller)
A VIDEO input port: 640dot(H) * 512dot(V) *8bit, it accepts NTSC signal.
Low power: The power-consumption rate is only
5W (+5V 1A).
Low cost: About 50,000 yen/module.

2 THE STRUCTURE OF THE SCSI-VME
MODULE
Figure1: VME-base data-acquisition system

1

CHARACTERISTICS OF THE SCSIVME MODULE

The SCSI-VME module is shown in Fig. 2. Themodule consists of 2 FPGAs (Field Programmable GateArray) and some TTLs. Although usually one such
module is used as a controller in a VME crate, more than
one module can be used in the same crate.
The specifications of the SCSI-VME module aresummarized below.

Figure 3 shows a block diagram of the SCSI-VMEmodule. The SCSI-VME module mainly consists of three
independent parts: namely, a SCSI-VME part whichtransfers data between SCSI and VME, a SCSI-GPIB port,
and a video capture port.
The module supports a subset of SCSI-command:
namely, Inquiry (12h), Write-VME (2Ah), Read-VME(28h), Write-GPIB or Write-VIDEO (22h), Read-GPIB orRead-VIDEO (20h), and Read-GPIB status (21h). If it
receives other commands, it always replies a checkcondition status code.

The first three commands are for the VME part. In
response to the inquiry command, it replies "SAT" asvender-identification, "VME" as product-identification,and "removable disk" as type. The Write- and Read-VME
command takes two operands: namely, 16-bit transfercount and 32-bit VME address, and performs a datatransfer of the given number of bytes to/from the VME
memory from/to the VME address. If the transfer issuccessful, it returns a STATUS code of 00h (successful),and if not, 02h (CHECK CONDITION).
For the GPIB case, the Read-GPIB and Write-GPIB
command takes two operands: namely, 9-bit GPIB

address & signels

3states latch& buffer

VME P1
16bits data bus

address and bus status, and 4-bit transfer-count data. In
order to adjust the speed difference between the faster
SCSI and the slower GPIB port, it provides a 16-byte
buffer memory on the board. The Read-GPIB statuscommand should be used before actually reading thebuffer data by the Read-GPIB command.
By the Write-VIDEO command, the video signal at
the time is captured to the frame memory. By the ReadVIDEO command with one operand, 16-bit transfer-byte
count, the frame-memory data of the given number ofbytes are transferred to the PC.

GPIB signels

3states latch

3states buffer

GPIB
GPIB bits data bus

3states buffer
1~2V

8bits

reference

IC15
data bus
switcher

VME
encoder

GPIB
encoderinGPIBmemory16bytes

VME address
counter
32bitstransfercounter
16bitstransfercounter
16bitsSCSI
decoder

8bits

3states buffer

SCSI
decoder

8bits8bits

A/D converter
8bits

IC14

V inframe memory
260Kbytes

data busswitcher

IC14,15: XC4004A or XCS10SCSI bus

Figure3: Block diagram of the SCSI-VME module

3DATA-ACQUISITION SYSTEMCONFIGURATION

Fig. 4 shows a general view of the data-acquisition
system. We use 3He -gas filled neutron detectors of 1/2 or1 inch diameter at 10 atmospheres. The amplifier module
consists of eight charge-sensitive amplifiers and pulseshaping modules which have a shaping constant of 0.5 µsec.

3.1 TA system
This system consists of an AMP module, TA modules
and a PC. Each AMP module receives 8 detectors. The
detector is single-ended. A bias voltage of 1000-1500V isapplied to the detectors. The output analog signal istransferred to the TA module by a twisted-pair flat cable.
The TA module has discriminators at the front-end andthe digitized timing signals are stored in histogram
memories in the same module.

3.2 PSD system

3.3 The SCSI-VME module and PC

We use PSD’s having a 1/2 inch diameter and a 607mm effective length, made by Reuter-Stokes. The
resistance of the anode wire of the PSD is about 4k •, andbias voltage of 1500-2000V is applied to the detectors.
The signals from both ends of a PSD are fed to chargesensitive preamplifiers and shaping amplifiers. Theposition is determined by a charge-division method.
This system basically consists of a PSD unit, PSD
modules and a PC. Each unit holds 8 PSD's, and many
units can be lined up so as to cover a large area with verythin gaps between the detectors. The PSD modules
encode the position and time, and histograms are made bythe PC.

The acquired data are then collected by the PC throughthe SCSI-VME module. Although we are mainly using
Macintosh computers made by Apple, we are also using
PCs running a Windows 98 or 95 operating system. The
entire controlling software is based on a commerciallyavailable package software, LabVIEW, from National
Instruments Inc.

PC
DataAcqusition
Software(Lab View)

SCSI
Macintosh or windows95

SCSI-VME module
TA modules
PSD modules
VME rack

to other SCSI
instruments

t=0 signal

3 He detectors

AMP module

high voltage 1000V ~ 1500V

high voltage 1500V ~ 2000V

PSD unit

Figure4: General view of the data-acquisition system

REFERENCES[1] S. Satoh and M. Furusaka, "International Workshop
on Data Acquisition Systems for Neutron
Experimental Facilities",DANEF’97, Russia, June1997[2] S. Satoh, T. Adachi and M. Furusaka, "Developmentof Data Acquisition Electronics System for Neutron
Scattering Experiment" (in Japanese), KEK Internal96-14, 1996
[3] S. Satoh and M. Furusaka, "Development of 8-Input
Amplifier and Multi-Channel Time-Analyzer Module
for Neutron Scattering Experiment" (in Japanese),
KEK Internal 92-4, 1992