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SET Instruction

Created by: Kriztof at: 6/13/2010 5:38 PM (8 Replies)

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6/13/2010 5:38 PM	Rate (0)
Kriztof Posts: 12 Rating: (0)	Could anyone explain to me why there are SET instructions at the beginning of the networks? I don't understand this concept. Network 1 SET A M 2.3 JCN M00 CALL FC 2 Slave :=MD12 Destination:=#Destination R M 2.3 M00: NOP 0 Network 2 SET A M 2.2 S M 2.3 S M 2.1 R M 2.0 Network 1 SET A I 0.0 FP M 3.0 S #Start
Kriztof Posts: 12 Rating: (0)
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6/13/2010 6:09 PM	Rate (0)
Berg Silver Member Joined: 1/17/2006 Last visit: 3/29/2023 Posts: 551 Rating: (29)	Kriztof Could anyone explain to me why there are SET instructions at the beginning of the networks? I don't understand this concept. Network 1 SET A M 2.3 JCN M00 CALL FC 2 Slave :=MD12 Destination:=#Destination R M 2.3 M00: NOP 0 Network 2 SET A M 2.2 S M 2.3 S M 2.1 R M 2.0 Network 1 SET A I 0.0 FP M 3.0 S #Start Hello Kriztof, Hello, SET instruction sets the RLO to signal state "1" and is used to "force" the RLO when you need, but in this case that makes no sense to me. I've seen too often use in the S7-200 the specially memory SM0.0at the beginning of the whole network, also without any sense to me. Maybe some expert can show us some sense of it. Best Regards.
	"Educate the children and it won't be necessary to punish the men." Pythagoras
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6/13/2010 6:13 PM	Rate (0)
pfuser Silver Member Joined: 9/18/2006 Last visit: 5/29/2023 Posts: 586 Rating: (64)	Hi. Probably it is feature of the compiler. Best regards.

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6/13/2010 6:26 PM	Rate (0)
Kriztof Posts: 12 Rating: (0)	This is full program maybe with right context it could be more clear. [url]https://support.automation.siemens.com/WW/llisapi.dll/csfetch/20989875/20989875_S7BaseComm_XSEND_v10.zip?func=cslib.csFetch&nodeid=21118029[/url]
Kriztof Posts: 12 Rating: (0)
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6/13/2010 6:37 PM	Rate (0)
Saravana kumar Gold Member Joined: 2/6/2009 Last visit: 4/19/2023 Posts: 932 Rating: (117)	DearKriztof, Every instruction in STL needs the RLO of the previous line to execute the operation. For Ex: Wrong Logic: A M0.0 = Q0.0 A M0.1 = Q0.1 NOP 0 In the above logic, if the first operation is notsuccess (i.e Q0.0 is false). The Q0.1will not get on even the M0.1 is High. Because the RLO of the previous is 0. Correct Logic: A M0.0 = Q0.0 SET A M0.1 = Q0.1 NOP 0 In the above logic Q0.1 will get ON if M0.1 is high irrespective of Q0.0, because the RLO of the previous line is set by the SET instruction. The set instruction to be used inside the network, But it is not necessary to use in the starting of the network/
	Last edited by: Saravana kumar at: 6/13/2010 6:41 PM Last edited by: Saravana kumar at: 6/13/2010 6:40 PM _______________________________________________________________ Best Regards T.Saravana Kumar "All for the Best"
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6/13/2010 6:48 PM	Rate (0)
Kriztof Posts: 12 Rating: (0)	Dear Saravana kumar I' ve just tested your sample codes, and they work identically. In the first example if M0.1 is true then RLO is also true so Q0.1 is true as long as M0.1 is "ON".
Kriztof Posts: 12 Rating: (0)	Last edited by: Kriztof at: 6/13/2010 6:56 PM
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6/13/2010 8:57 PM	Rate (0)
yy1 Gold Member Joined: 3/24/2009 Last visit: 1/5/2023 Posts: 535 Rating: (110)	Dear Kriztof, after the '='-instruction, the SET-instruction is not required necessarily, because it sets the /FC-bit (First Check Bit) to 0. So the next instruction-string will start with a first-check. /FC First Check Bit (Status Word, Bit 0) The /FC bit signal state controls a logic operation string. The /FC bit is status word bit 0. Each logic operation queries the /FC bit signal state and the addressed contact. · If the /FC bit signal state equals ‘’1,’’ an instruction logically combines the result of its signal state check on its addressed contact with the RLO generated since the first check and stores the result in the RLO bit. · If the /FC bit signal state equals ‘’0,’’ the logic string begins with a first check. The logic string ends and the /FC bit is set to ‘’0’’ with the assignment of a value (S,R,=) or with a RLO-dependent jump instruction. However the SET makes the logic clearly arranged. Best regards, yy1

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This contribution was helpful to 1 thankful Users Berg

6/13/2010 10:14 PM	Rate (0)
Kriztof Posts: 12 Rating: (0)	OK this is my theory.A instruction need two arguments to calculate properly RLO, I think the first argument is STA bit (actual bit) and the second is RLO (from previous logic operation) then new RLO is calculated. So SET instruction is the only "empty" instruction that can turn on RLO bit at the beginning of the network without unexpected results. Network SET // STA=1, RLO=1 A M0.0 // let’s assume M0.0 is 1 then 1 1 = 1 (RLOSTA= new RLO) = Q0.0 //then Q0.0=1 (=RLO) Maybe it is something, as mentioned before, with older compilers or older CPUs. What do you think guys? Network A M0.0 // let’s assume M0.0 is 1 then 1 0 = 0 (RLOSTA= new RLO) = Q0.0 //then Q0.0=0 (=RLO)
Kriztof Posts: 12 Rating: (0)	Last edited by: Kriztof at: 6/13/2010 10:26 PM
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6/13/2010 10:58 PM	Rate (0)
fritz Diamond Expert Joined: 10/7/2005 Last visit: 6/3/2023 Posts: 2966 Rating: (1025)	Kriztof Could anyone explain to me why there are SET instructions at the beginning of the networks? I don't understand this concept. Hello Kriztof here's my two cents worth on this subject: Whoever programmed it, did it"to be sure to be sure". Similar to what yy1already explained, as long as the previous RLO is "closed" (which an "=", "S", "R" and/or conditional Jump instruction will do), there is no need to additionally use a "SET" (to "force" the RLO) before you start a new RLO (it is an overkill, albeit one that does not do any harm other than costing memoryandscan time). Have a look at THIS thread too for some more detailed info on the subject of the "/FC" bit. I hope this helps
	Last edited by: fritz at: 6/13/2010 10:59 PM Cheers fritz The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited. To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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This contribution was helpful to 2 thankful Users Berg yy1

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