[Binary Read Request - Ambigious responses for Memory Bit read request]

Hi, I hope you might help with the following issue:

I wrote  a simple python library, using the PCOM protcol &  pySerial. To test it,  I created a script that reads a few Memory Bit operands from a SM-43 via the built-in RS232-USB Bridge. The library and the script work perfectly, accept when it comes to reading more than seven bit operands:  I used the online mode to set the MB100-107 to the values : 10101100.  While the response comes back intact, ( checksum checks out etc) I'm getting different responses  for the same request.  The respective bytes in the payload of the response message vary between:

• 0x3521
• 0x3523
• 0x3544
• 0x3543
• 0x35cb

Note that

1.  I made sure that the actual bit values in MB100-107 do not change
2. The response is consistent, as long as I don't change the status of MB107. However, as soon as I'm toggling MB107 on and off again, i get a different response from the PLC afterwards. I also get a different response when I change the read request and then go back to the old read request.
3.  The first seven bits do not seem to be affected by this - They show 0x35 consistently.

Maybe I overlooked something?  Thanks in advance for any hint!

Max

 

 

[Fatal Error Ldr 0x00003fb0]

Hi,

One of our local supervisors sent me the following picture of this error message appearing on the screen.  Restarting solved the problem for the moment, nevertheless, I'm curious what this error might be, just to make sure that it is not a systematic error. I am not a very experienced PLC- programmer, so any help is very much appreciated.

Thanks

Max