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OUT variable update at block call??

Created by: Thijs at: 6/29/2006 10:01 AM (11 Replies)

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6/29/2006 10:01 AM	Rate (0)
Thijs Posts: 121 Rating: (15)	I'm now looking into a program where there are standard defined block for some simple track controll. No problems so far. I've only notised a behaviour I didn't see before. There is an OUT parameter declared and it's used as an IN_OUT. Let me show an example: FC83 +-----------------+ \| IN: \| M5.0 \| bSTART \| M5.2 \| bSTOP \| \| \| \| IN_OUT \| \| \| \| OUT \| \| bRUN \| M5.3 +-----------------+ And the code looks like this: bSTART bSTOP ------\| \|-----\|------\|/\|---------(bRUN) bRUN \| ------\| \|-----\| I allways believed that the "bRUN" than must be declared as an IN_OUT. Is this a correct ussage off the "bRUN" parameter??
Thijs Posts: 121 Rating: (15)
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6/29/2006 11:06 AM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 6/5/2023 Posts: 4179 Rating: (644)	No.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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6/29/2006 12:51 PM	Rate (0)
Thijs Posts: 121 Rating: (15)	Why does it work than?? I was amazed when I saw this programming. But I don't know for sure if it's correct. The machine is running now for 5/6 year I think --update-- I've just ran a test in PLCSIM, and it WORKS!! Please can someone tell me what I don't understand
Thijs Posts: 121 Rating: (15)	Last edited by: Thijs at: 6/29/2006 12:57 PM
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6/29/2006 1:00 PM	Rate (0)
Tomcat Posts: 433 Rating: (48)	Hello Thijs, could you insert a screenshot ofthis call or the source of the block? Tomcat
Tomcat Posts: 433 Rating: (48)
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6/29/2006 1:24 PM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 6/5/2023 Posts: 4179 Rating: (644)	In case of a FC whole interface is placed in the local data area. It means that before execution assigned values are copiedto input variablesand after execution output variables are copied to their destination. As long as the local data can hold interfaces of all blocks one may think that the local data are preserved between scans because an interface of a block is always in the same place of the local data area. And in such a case this example works. But if it's not a case then blocks are given areas with undefined contents of TEMP and OUT area. Then reading them before writting gives "amazing" effects. And this is explicitly stated in the manuals for S7.
	Last edited by: jacek d at: 6/29/2006 1:27 PM Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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6/29/2006 1:30 PM	Rate (0)
Thijs Posts: 121 Rating: (15)	The funny thing is, that there several blockcalls in the program, all calling the sam FC, but with different parameters. The machine works, but as stated here, it is not a relyable system tho. Attached the example I've made. I've made 2 calls for the same block, still it does what I think it should do. Tomorrow I'm with the machine again, will talk with the local programmers Attachment Test OUT blockcall.zip (221 Downloads)
Thijs Posts: 121 Rating: (15)
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6/29/2006 1:41 PM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 6/5/2023 Posts: 4179 Rating: (644)	Possibly each FC call gets its own "context" in the local data area.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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6/30/2006 8:44 AM	Rate (0)
Tomcat Posts: 433 Rating: (48)	Hello Thijs, I have viewed your source and the picture. FC1 will used to control (start and stop) different units, but the way of doing of this controlling is the same. This code A( ; O #bSTART; O #bRUN; ) ; AN #bSTOP; = #bRUN; means: if the unit should be started or is running already (information from last cpu-cycle) and it should not be stopped, then set "Running". Regards Tomcat
Tomcat Posts: 433 Rating: (48)
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6/30/2006 10:14 PM	Rate (0)
Thijs Posts: 121 Rating: (15)	Tomcat, Programming is not the issue, I've posted an example to clearefy my problem. Today I've changed all OUT "memory" into IN_OUT declarations. so in my example the "bRUN" is now a IN_OUT. thanks a lot
Thijs Posts: 121 Rating: (15)
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7/4/2006 8:47 AM	Rate (1)
Dec Gold Expert Joined: 5/19/2006 Last visit: 6/5/2023 Posts: 547 Rating: (106)	Hi Thijs, From the PLC point of view for FCs there is no difference between IN_OUTorOUT. All are pushed into the stack before the function isexecuted (UC FC1). Actually STEP7 wraps the CALL FC1 by pushing all IN, OUT, IN_OUT variable pointers into the stack and thenexecute UC FC1 instruction (parameters are passed by reference not by value using the stack): UC FC 1 P#M 0.0 //bSTART P#M 0.1 //bSTOP P#M 0.2 //bRUN Inside your FC1 you actually read/write using those pointers. In LAD there is a slightly difference when call FC1 where IN parameters are buffered in L area: A M 0.0 = L 20.0 BLD 103 A M 0.1 = L 20.1 BLD 103 BLD1 = L 21.0 UC FC 1 P#L 20.0 P#L 20.1 P#M 0.2 BLD 2 NOP 0 Dec
	Last edited by: Dec at: 7/4/2006 8:54 AM
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