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multimeter protocol

Dear All,

I have a Mastech MS8220T multimeter that I want to hook up to a PC. It has a serial interface and the included program runs fine, but the protocol is not documented. I had a look at the output with a scope, looks like 9600 baud, but there are some bits that are too short for that, they have a bit less than 50 us duration. Maybe these are the stopbits, signal quality is very bad and it's difficult to identify the individual bits. Do you have any Idea how to guess the protocol and rs232 settings? Is there any way to identify the port settings if I have the software running (xp) ? I had a look at the standard 7 segment encoding, but this does not seem to be used. Even if the disply shows a constant value several different codes are transmitted.

Any ideas?

Reply to
rubbishemail
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Dirk

http://www.transcendence.me.uk/ - Transcendence UK
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Reply to
Dirk Bruere at NeoPax

At 50uSec I doubt that are anything.

They may be using a bit-banged serial port and that may be the software glitching the I/O port.

Get two extra serial port on your machine and run multiple copies your some terminal program at 9600 baud in hex mode.

Each serial port connected to each pin of the meter serial port.

Shouldn't be too painful.

donald

Reply to
donald

Hi Dirk,

thanks a lot for your link, the device monitoring studio did it in less than five minutes. Here are the settings for the Mastech, in case anyone should have the same problem: Baudrate: 19200

7 bit 1 stop Odd parity

I never would have imagined this speed. The data is transmitted as plain ASCII and has the form

m is the multiplier 0 for mV, 1 times 10, 2 times 100 n are the four digits x give sign, range etc for DCV it is ;80: for pos ;

Reply to
rubbishemail

Hi Donald,

when I hooked up the scope the additional loading was already too much to stop the thing from working, so probably it wouldn't work with an extra port either, therefore I didn't even try. This is the first DMM I've seen that runs at such a high speed, I thought the 50 us were glitches as well, because the signal looks very bad, already the 104 us (now I know two bits...) are barely defined.

Daniel

Reply to
rubbishemail

Either you really screwed up your connecting the scope, or this is not RS-232.

Do as Donald suggests, that is a valid, and easy thing to do. If it doesn't work because the second monitoring port loads the device too much, then it is not RS-232.

Reply to
PeterD

probably it is not true rs-232, the DMM contains a photoemitter and the plug a photodiode and three transistors. Does not matter, works good enough now. With the right port settings it was easy to guess.

Thanks

Daniel

Reply to
rubbishemail

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