Ascii interface with A&D balance

PLChristian

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May 2021
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Wisconsin
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Hi everyone. I am trying to interface a balance and a AB compact logix L24ER with a 1769-ASCII card. I am using a rs232 connection between the devices. I would just like to display the weight from the balance into Studio 5000. Does anyone have experience with programming these ASCII cards?
 
Welcome to the PLCTalk forum community !

Please provide some more information, like a product page or user manual, for the "A&D Balance".

ASCII strings are pretty straightforward in Logix 5000 and with that module, but I'm not familiar with the exact device you're working with.
 
I have a code that works how ever I am confused when it comes to interpreting the data.
In my program I am able to observe the RXdata change however in my array the data points change from 120 to 0 when I weigh different masses on the balance.
 
Have you tried using a simple coms program to see what data is being transmitted, most scales will be capable of giving out an ASCII string with possible start char, address & end char, possibly a simple char print for interface for a printer, are you sure you have the 232 parameters set right i.e. Baud, parity etc.
 
I'm with Parky, use Putty or something similar and send the ascii to your laptop and view the string in real time.
Once you know exactly what is being sent, you can then work on getting the receive end correct.
 
Bzzzzt! No, thanks for playing ;-).

My money is on a mismatch of baud rate between the balance and the PLC. But it could be parity or stop bits.

Hook the balance up to a PC with a serial port or USB-serial interface, and fiddle with with the COM port settings in Putty or HyperTerminal (does that even still exist?) until you see the strings that match what the manual says are being sent.
 
ASCII lowercase x = 0x78 hex = 120 decimal = 0111 1000 binary

That doesn't look like a parity or baud rate mismatch to me.

All the strings in the various output formats end with <CR><LF> , and I don't see them anywhere.

https://weighing.andonline.com/sites/default/files/documents/(Revised) Communication Manual.pdf

The usual troubleshooting tool I use is RealTerm, because it's so much easier to connect TCP, or USB, and change the framing and serial settings than it is to change them on a PLC.
 
I've done this using the Local Serial Port on a L32E but not with the ASCII card.
Does the card require you to use standard ASCII commands?
How quickly are you trying to read the Data?
Is it in Print Mode or are you asking it to send you the Weight?
 
I did have a mismatch between baud rates, however after setting them both to 9600 the data I receive now is all on value and does not change when I weigh different masses on the scale. I am confused with the crlf data and what that is used for as well as what parity it should be
 
Usually a data rate mismatch gives all zeroes or all ones, resulting in values like 0xFF and 0x7F and 0x00, but of course "unpredictable" results are unpredictable.

The new character is shown in RSLogix 5000 as "$l" (lowercase L) which is 0x0A = <Line Feed>

So at least that suggests the balance is sending all line-feed data !

Let's see the rest of the logic that reads the ASCII strings from the serial buffer and determines their length.
 

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