Newsgroup: it.hobby.fai-da-te
Titolo: Calibro Digitale con Data Out - to PC - Data Sheet.

Per quelli pi� "ferrati" in Elettronica Trasmissione Dati...
Ecco le caratteristiche di un Calibro Digitale Standars
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Four-key Digital Calipers With Data Cable ,
Series:EC20
FEATURES
 Four-key Digital Caliper
* Large and clear LCD readout.
* Power on/off.
* Zero-setting at any position.
* inch/mm switch.
* Stainless steel.
* Include two 1.5V button batteries which are easy to replace.
Data Cable
Data output Port:
COM port
RS232C port
Power: Via PC
Interface Protocol:
Baud Rate: 4800 Data Bits: 8 Stop bit: 1. No correction or examination.
Data will be sent inASCII Code (and TXT) continually.
After each datum finishes sending, press.There's no frame for data.
Code ASCII for data measurement consists of 10 bytes starting with sign 
<+>or sign <->, followed by 7 digits, one decimal point and .
With stable bytes transmission.
Followed by a group of data is Code ASCII for .
Transmission Rate: 300ms/ each time
*Signal Cable:2 m

 Per quelli pi� "ferrati" in Elettronica Trasmissione Dati...
 Ecco le caratteristiche di un Calibro Digitale Standard
NON ho disponibile lo Schema Elettrico.
 
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The Chip of digital calipers.
The electronic digital caliper for computer (RS-232) interface will work the 
inexpensive calipers, micrometers and height gauges.
There are 4 pins on the connector of the measuring instrument, and the 
owner's manual will typically describe the output as 24 bit 90 kHz 
synchronous.
The code contains examples of:
. 9600 bps asynchronous receiver/transmitter
. 90 kHz synchronous receiver
. Host command processing
. Tables for data and text
. Sending text to host
. 24 x N bit fractional multiplication
. 24 bit addition
. Binary to BCD conversion
. BCD to ASCII conversion
. ASCII transmission with leading zero suppression and fixed decimal place
. Operational mode set by jumpers or override by host
. Use of watchdog timer
The circuit contains examples of:
. +5V/-1.5V power from serial port
. 1.5V to 5V logic level conversion
. minimal PIC to RS-232 interface
The caliper will send a burst of data about three times each second. Each 
burst contains 48 bits of data, and the first 24 bits are the position 
relative to the zero point which is set on the caliper.
The second 24 bits are the position relative to an arbitrary zero that does 
not change.
This is a kind of an absolute position, but the zero point changes each time 
the caliper loses power.
Each 24 bit value is in ones compliment form (1 sign bit, 23 data bits).
This allows for a 0 and a -0. The unit of measure is 1/20480th of an inch.
Usually, the caliper is powered by a small 1.55 volt battery, and the 
positive of the battery is connected to the metal parts of the caliper 
making it positive ground.
The logic levels are -1.55 volts low and 0 volts high.
The clock and data signals from the caliper are AC coupled by C1 and C2.
The AC coupling effectively moves the logic levels above ground so they can 
be easily converted to standard CMOS logic levels (0 and +5 volts).
Three gates of IC1 are used as a 3.3x linear amplifier.
The amplifier is driven to saturation by the low logic levels from the 
caliper.
The data and clock signals are then sent to the 12C509 microcontroller.
The microcontroller firmware has a synchronous receiver that handles the 
burst of data from the caliper.
In binary mode the 48 bits are sent to the computer literally.
For inches or mm mode the first 24 bits are scaled to real units.
The raw value is multiplied by 125/256 for inches or by 127/1024 for mm.
The result is then converted to BCD, then converted to ASCII and sent to the 
host computer.
Sign and decimal are handled within the BCD to ASCII conversion routine.
The asynchronous transmitter is implemented in the firmware like the 
synchronous receiver.
While idle the interface checks for data from both the host computer and the 
caliper.
The first one to initiate communication gets the full attention of the 
interface.
The host computer should send a 10ms break to get the attention of the 
interface.
Then a '?' will be send to the host when the interface has seen the break 
and entered command mode.
The most common commands issued are 'I' for inches, 'M' for mm, or 'B' for 
binary.
The initial mode is set by jumper block JB1 pins 1,2,3 and 4.
The interface will remain in command mode until an 'E' is sent to return to 
normal operation.
Power for the interface and optionally the caliper is supplied by the host 
computers' RS-232 port.
The RTS and DTR line supply power through D1 and D2 to voltage regulator 
IC3.
The regulated 5 volts from IC3 is supplied to the 12C509 microcontroller 
(IC2) and the 4049 hex inverter (IC1).
D3 is normally not used. Power for the caliper is supplied from the host 
computers TxD line.
Since this line changes state while in command mode, C5 stores enough energy 
to power the caliper during those times.
Diode D4 prevents the C5 for being discharged.