RS Flip Flop according to IEC 61131.Who is correct? ABB or Siemens? Quite interesting.....

[Preet 0]

This is what I got from ABB Control Builder Help file about RS flip flop: How to Use the Function Block The RS bistable flip-flop, is a latch where the R1 input dominates. If the Set and R1 signals are both True, the output Q1 is False. Specified in the IEC 61131 standard This is what I got from S7 Help file about RS flip flop: Description The Reset_Set Flip Flop instruction executes instructions such as Set (S) or Reset ® only when the RLO is 1. An RLO of 0 does not affect these instructions, the address specified in the instruction is not changed. Reset_Set Flip Flop is reset when the signal state at input R is 1 and the signal state at input S is 0. If input R is 0 and input S is 1, the flip flop is set. If the RLO at both inputs is 1, the flip flop is set. The Reset_Set Flip Flop instruction is affected by the Master Control Relay (MCR). For more detailed information about how the MCR functions, refer to MCR on/off. I guess both the explanations are different from each other.Can anyone tell me the exact definition of RS block according to IEC standards. Thanks Preet

[Gazzr 0]

In S7-200 software there are two Set/Reset instructions. The only difference between them, being the conditions you have described. If both inputs are true, one of them would be in the Set state, while if you used the other instruction it would be in the Reset state. Do they not have something similar in Step 7?

[Moggie 17]

Step 7 has two instructions the SR "flip Flop" and the RS "Flip Flop". From the Step 7 Help files; SR (Set-Reset Flip Flop) is set if the signal state is "1" at the S input, and "0" at the R input. Otherwise, if the signal state is "0" at the S input and "1" at the R input, the flip flop is reset. If the RLO is "1" at both inputs, the order is of primary importance. The SR flip flop executes first the set instruction then the reset instruction at the specified <address>, so that this address remains reset for the remainder of program scanning. RS (Reset-Set Flip Flop) is reset if the signal state is "1" at the R input, and "0" at the S input. Otherwise, if the signal state is "0" at the R input and "1" at the S input, the flip flop is set. If the RLO is "1" at both inputs, the order is of primary importance. The RS flip flop executes first the reset instruction then the set instruction at the specified <address>, so that this address remains set for the remainder of program scanning.