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Old December 2nd, 2009, 03:22 AM   #1

lakshmi.chamarthi is offline
Join Date: Jun 2008
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Omron Modbus PMCR

I have the Omron CJ1M CPU and SCU31-V1 module for Modbus with Protocol Macro using PMCR instruction in the ladder. Here PLC is the master and Remote I/O cards are slaves. We have 13 Remote cards/slaves.

Is any other method for Modbus PMCR polling other than using a counter?
Time b/n polls or pollrate on a slave in 13 slave network is 1.5sec. I want to reduce this time.

Last edited by lakshmi.chamarthi; December 2nd, 2009 at 03:24 AM.
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Old December 2nd, 2009, 08:40 PM   #2
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BobB is offline
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I use a counter for this always.
There are 3 things that slow down polling - number of devices - size of poll and comms speed. Increase the speed and decrease the time - decrease the number of polls and decrease the time - decrease the size of the poll and decrease the time.
I normally poll a maximum of 4-5 devices at a minimum speed of 19,200 baud. I find it is quicker to do 2 polls to a device sometimes. If I want 3 words from one area and 3 words from another area it is usually quicker to do 2 polls for the 3 words each time than poll 50 words top get the same information in one block with a lot of other rubbish.
The SCU31 has 2 x RS485 - break the network into 2 and use both ports.
The Old Pfhaart

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