.....I know how it works in the modicon, but in rslogix, using Latch/Unlatch seems a bit excessive. When the rung loses Power, output goes off, but when the controller loses power, output stays on for one scan unless conditions are still true...
That is not a correct statement, or I read it wrong...
All A-B processors have 3 bit/bool output instructions that write to a single bit of memory. These are OTE, OTL, and OTU.
A "Pre-Scan" of all of the logic is performed at power-on, or a transition into RUN mode - the pre-scan affects non-retentive bit addresses.
OTE - during normal program scan, the associated address will be turned ON (written to a "1") by a rung that evaluates as TRUE, and turned OFF by a rung that evaluates as FALSE. In addition, bit addresses attached to OTE instructions will be automatically reset to zero during the processor pre-scan. Rung logic will therefore determine whether the bit address will be turned ON (true logic), or turned OFF (false logic). Addresses attached to OTE instructions are therefore "non-retentive".
OTL - during normal program scan, the associated address will be turned ON (written to a "1") by a rung that evaluates as TRUE. OTL will never write a "0" to the bit address. In addition, bit addresses attached to OTL instructions will not be automatically reset to zero during the processor pre-scan. Addresses attached to OTL instructions are therefore "retentive".
OTU - during normal program scan, the associated address will be turned OFF (written to a "0") by a rung that evaluates as TRUE. OTU will never write a "1" to the bit address. In addition, bit addresses attached to OTU instructions will not be automatically reset to zero during the processor pre-scan. Addresses attached to OTU instructions are therefore "retentive".
If a program has both retentive AND non-retentive instructions attached to the same bit address, then that address becomes non-retentive, since the pre-scan will reset it to "0".
HTH