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STEP 7 programing in CFC

12/9/2009 7:56 AM	Rate (0)
ab1234 Posts: 9 Rating: (0)	I am a new user of Step 7 software. I have understanding that the analog I/Os, like Digital I/Os,are not scanned and updated during PI updation. Is it true? Every time analog value is required in program, it is mandatory to load the value from I/O module via Load instruction? Thanks
ab1234 Posts: 9 Rating: (0)
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12/9/2009 4:52 PM	Rate (0)
Phantom75 Posts: 2661 Rating: (279)	Hi ab1234, In the olden days with STEP5 CPU's, due to memory limitations only the digitalI/O area was assigned a process image (PI)address space. This may also be the case now in lower end S7 CPU's. But with higher end S7 CPU's the address space is virtually unlimited. It is customary (especially with PCS7/CFC)to assign the entire address space a process image and furthermore split the PI area into different updatespeeds as needed. Regards
Phantom75 Posts: 2661 Rating: (279)
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12/14/2009 1:18 PM	Rate (0)
ab1234 Posts: 9 Rating: (0)	You mean when we address PIW XX, we are calling data from PI and not from I/O module directly.
ab1234 Posts: 9 Rating: (0)
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12/14/2009 11:31 PM	Rate (0)
Phantom75 Posts: 2661 Rating: (279)	Hi ab1234 When we address as PIW xx we are directly reading from the periphery (I/O module). When we address as IW xx we are reading from the PI area. PI area gets updated every OB1 cycle (default) or other OB cycle (set by user). In PCS7 we seldom useperiphery addressing especially when using redundant I/O. Regards
Phantom75 Posts: 2661 Rating: (279)
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12/15/2009 8:32 AM	Rate (0)
ab1234 Posts: 9 Rating: (0)	Hi Phantom75 Thanks a lot for the clarifications. See u again
ab1234 Posts: 9 Rating: (0)
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