Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 339)

Chapter 25
Control Instructions
25–7
This output instruction marks the end of subroutine execution or the end of
the subroutine file. It causes the processor to resume execution in the main
program file at the instruction following the JSR instruction where it exited
the program. If a sequence of nested subroutines is involved, the instruction
causes the processor to return program execution to the previous subroutine.
The rung containing the RET instruction may be conditional if this rung
precedes the end of the subroutine. In this way, the processor omits the
balance of a subroutine only if its rung condition is true.
Without an RET instruction, the END statement (always present in the
subroutine) automatically returns program execution to the JSR instruction in
your calling ladder program.
SLC 5/02 processors: Use the RET instruction to terminate execution of the
STI subroutine (chapter 30), I/O event-driven interrupt subroutine (chapter
31), and the user fault routine (chapter 29).
Master Control Reset MCR Output Instruction
(MCR)
(MCR)
F1 F2 F3 F4 F5
ZOOM on MCR –(MCR)– 2.3.0.0.2
NAME: MASTER CONTROL RESET
EDT_DAT
HHT Ladder Display:
HHT Zoom Display:
Ladder Diagrams and APS Displays:
(online monitor mode)
The master control reset instruction is an output instruction, used in pairs. It
lets the processor enable or inhibit a zone of a ladder program according to
your application logic. Instruction parameters do not exist for the MCR.
You start the zone with a conditioned MCR instruction. When the MCR rung
is false, all non–retentive outputs in the zone are disabled. The processor
scans all output instructions within the zone as if they were false. When the
MCR rung is true, outputs act according to their rung logic as if the zone did
not exist. You end the zone with an unconditioned MCR instruction. You
cannot nest MCR zones.
Important: Do not jump (JMP) into an MCR zone. Instructions that are
programmed within the MCR zone starting at the LBL
instruction and ending at the “End MCR” instruction will
always be evaluated as though the MCR zone is true, regardless
of the true state of the “Start MCR” instruction.
Master Control Reset
(MCR)