Product: ISaGRAF V3
File: Wdkcomer.Communication and synchro errors with ISDK_COM.DLL.htm
Subject: Communication and synchro errors with ISDK_COM.DLL
Keywords: ISDK_COM - synchronization - communication - error
Below are the main reasons that can lead to a communication error:
1- Time out: this can be checked easily by setting a very long time
out from the workstation (ex 10 seconds).
2- A communication error appears if you answer something else than
0 in the "errcode" return parameter of the isdk_com_receive
routine. The best would be to place a trace in your ISDK_COM
software to detect such cases.
3- It can also be a synchronization error, if questions and answers
does not match. To ensure this, you can trace the second byte of
sent and received packets that cross the ISDK_COM layer. Below
is the meaning of first bytes in snd_data and rcv_data packets
handled by isdk_com_send and isdk_send_receive:
function code (normally greater or equal to 65)
A couple of (send,receive) packets must have the same packet number.
You can trace these bytes to ensure that there is no synchronization
Communication error is normally the only way to jump from "run/stop"
state to "application active" state. If you do not discover anything
with previous tests, you should trace the complete contents of
exchanged packets (questions + answers), during a period that covers
a strange change of state in control panel.
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