Wdkcomer.Communication and synchro errors with ISDK

Product: ISaGRAF V3

Date: 5-March-1996

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

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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)

packet number

(other bytes...)

A couple of (send,receive) packets must have the same packet number.

You can trace these bytes to ensure that there is no synchronization

error.

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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