RSLogix 5000 MSG Instruction

B

Thread Starter

Bill Overton

I am currently using Ver 8.0 of RSLogix 5000. I am using 6 MSG instructions to read a block of data (CIP Data Read) from 6 different IP devices. Currently, I have a bit that gets shifted every 15 seconds in a register. When the bit reaches a designated position, then one of the MSG instructions is enabled. This means it takes 1 1/2 minutes to complete the reads for all 6 devices. If I descrease the shift time then I tend to get read errors. Is there a more efficient and faster way to read data from IP devices?
 
Here are two approaches to Allen Bradley MSG that I have succesfully used:

1) First reset and enable all MSG blocks. The PLC queue will handle multiple MSG's simultaneously. When all MSG blocks have returned a DONE or ERROR bit, start a timer and then reset and enable the MSG's again (this approach is in the AB SCADA application manual).

2) Similar to above, but use a repeat cycle timer to reset and enable the MSG's. I have observed that MSG's sometimes do not return a DONE or ERROR bit.

Hope this helps.
 
Are you energizing the msg for the full 15 seconds?
If so you may want to reduce that time. Typically I only energize a messege for 1 second or less.
This would allow you to speed up your BSL.
 
D

DAVCO Automation

Check the need for something like a false to true transition or one-shot it sometimes AB doesn't reset done bits until a transition takes place and if your timer is staying "enabled" the message will not re-fire.......you should get much much faster message times than this....we do..........

Shooting from the hip without seeing what you are doing.

Dave
 
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