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| 1/20/2012 1:17 PM | |
Joined: 10/7/2005 Last visit: 9/10/2025 Posts: 3049 Rating:
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Hello Jeebs my understanding is that the data can be updated at any moment in the cycle in your S7-400, but I'm afraid to say that I can't provide any Siemens "proof" for this (WW however has Technote 304 about this and I can assure you that WW InBatch withDASSIdirect will write to the PLC memory at any moment in time with an S7 400/Ethernet CP combination). Note that newer300 CPU's now allow a tick mark in their HWconfig properties for "Prioritized OCM communication". If ticked, they'll behave like 400's a far as comms value updated is concerned (i.e. they can change at any time in the cycle, see HERE for more). That's my take on things anyhow and perhaps others can verify or correct thisview. I hope this helps P.S.: There's an easy way to test the udpate behaviour: Configure a button on the HMI that simply sets a (free) bit in the PLC. Program a simple "if bit ON, add 1 to an MWvariable and reset bit" instruction at the start of OB1. Add essentially the same instruction at the end of OB1, but use a different MW to increment. Make sure to have a bit of logic in between the two (to get some OB1cycle time) and test it. If the update does take place at any moment in time during the scan, you'll see the MW at the end of OB1 count up (which is what I would expect to see). Let us know what you find. |
Last edited by: fritz at: 1/20/2012 1:31 PMAdded P.S. Cheers |
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