Slow Communication - nModbus RTU to DL05

Hello,

I would like some suggesting to debug slow RTU communication using nModbus. I have tried Google without much success and i thought i would throw this out before the weekend.

I have a C# HMI i wrote that uses nModbus RTU to communicate to a Direct Logic 05-DD plc.

The HMI updates on a timer tick the status of inputs, outputs, the internal coils that i am using, a counter current value, and a timer current value. Each is checked through its own method, one for inputs, one for outputs, etc.

I can't seem to set that timer tick faster than 650ms or it really bogs down the whole form. I checked the scan time of the plc ladder logic and its between 20 and 30ms, but each request to the plc take 300 - 400ms to return.

current setup is using a baud rate of 9600. Increasing the baud rate to 19200 didn't make any difference.

Thank You.

I assume the requests are sequenced one at a time? I would normally assume reasonable length requests would be answered within 1or 2 scans.

But I'm not an expert in using the DL system as an RTU server, only as a client with the DL06.

Yes. Each request is inside a method and each method is called one at a time.

I also assumed that the request would be answered within a scan or two of the plc receiving it.

This is the C# code i am using to handle the request. the test variable is a stopwatch that i have been using the check the response time.

private void plcUpdateTimer_Tick(object sender, EventArgs e)
{
if (i == 1)
{
test.Reset();
test.Start();
ReadInputCoils();
test.Stop();
}

else if (i == 2)
{
ReadOutputCoils();
}

else if (i == 3)
{
ReadSpecialCoils();
i = 0;
}

i++;
}

Well i tried to edit the code to make it more readable but i have very little experience with html. Sorry.