Citect, MODBUS RTU, and False Data

OK, I've come upon an interesting phenomenon, and I thought I'd run it by everyone here before I pester support. I've got a CitectSCADA system connected via MODBUS RTU to a controller. When it is running normally, everything is fine. Data is collected and displayed properly. However, if the computer, or just Citect, has to be restarted, when it comes back up it immediately has a bunch of incorrect data. After the first poll, the data goes to normal. This would not be that big of a deal, except for the fact that several of the pieces of inccorect data are alarms. Has anyone seen Citect do anything like this before? I'm trying to decide if this is an issue with Citect, the computer's COM port, the controller, or what. thanks in advance.

Joe

I have not used Modbus direct out of Citect before but normally take the Modbus data into a PLC first.

However, it is quite possible that Citect is getting up before the comm port is ready or something like that. I do not know if you can put a delay on the first read or not.

Support would probably be your best bet.

Try StartDelay

Hi jgreenewv,
I have a similar problem with Citect and Profibus Comms
to Siemens PLC's. I overcome it by putting a StartDelay of
30 Seconds in the citect.ini file. It is as follows:

[GENERAL]
StartDelay=30

It may not help but is worth a try.
Of course you may not need to delay as much as 30 seconds.

Good luck
John Gaunt

BobB and John,
Thanks for getting me pointed in the right direction. I actually ended up changing the StartTimeOut parameter under the [Com] section of citect.ini I tried the StartDelay under General, but didn't seem to make a lot of difference. So, I dug into the Computer Setup Editor (under 6.1), and found the [Com]StartTimeOut parameter. I set this to 5 seconds, and it seems to have cleared up the issue. Thanks again.

Joe