Host Engineering Forum
General Category => DirectSOFT => Topic started by: beauchemin on November 03, 2010, 12:11:13 PM
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Hi every,
We have a plc who's communicate with a c-more hmi and a delta motion controler. The communication is over ethernet and plc is the master.
The problematic rung was :
--|c1|---|\C3|---|\C5|---(c6)--
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--|C6|--|
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--|fs|--|
C1 is associated with a cmd in hmi and c6 with a light in hmi also.
When we push on hmi cmd C1 is activated and the light turn on, but c6 was never latched.
To check the desactivation was not append by c3,c5 and c6, we put a counter to verify events. Since, counter on c3 and c5 doen't increase and c6 increase.
This problem appear intermitentely. To solve problem, we need to reset plc.
We have also check the memory map to ensure of no overlapping addres.
If you have any idea,...
Thanks
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When I use bit communication from an HMI to a Direct Logic PLC I allocate 'C' bits in groups of 16, eg 00-17. One group is for bits which will be controlled directly by buttons on the HMI. Another group is for bits the PLC will change and are used by the HMI for display. You may try seperating your C1 (HMI button press) and C6 (HMI light, set by the PLC) into groups as I suggest.
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Thanks for fast reply,
I will try this solution then i will come back with result.
Have you any explanation about this behavior? Is it a know issue ?
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Most communication methods can't affect just one bit. To turn on a bit they have to read the entire word which contains it, turn on that bit, then send the entire word back. If, in the meantime, the PLC had decided to affect another bit in that word the 'write back' will overwrite that modification. It's not an 'issue' as such. it's just a fact of communicating.
So using a full 16 bits (when using 'C' bits that would be starting from a 'C' whose last number is zero and next to last number is even - like 40 or 60, not 30 or 51) is advisable. Again, devote 16 locations just for bits which be affected by the HMI. Leave others for those the PLC affects (though I tend to group those also).
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If your HMI uses K-Sequence, it can manipulate single bits. I'm guessing that's what you have configured your c-More to use. Modbus also supports writing to single bits. DirectNET protocol does NOT support writing single bits.