Chapter 9 Flashcards
override instructions
output type instructions that provide a means of executing sections of control logic if certain conditions are met
program control instructions
used to enable/disable a block of logic program or to move execution of a program from one place to another place
JMP
jump to label
jump forward/backward to a corresponding label instruction
LBL
label
specifies label location
JSR
jump to subroutine
jump to designated subroutine instruction
RET
return from subroutine
- exits current subroutine & returns to previous condition
- placed at end of subroutine
SBR
subroutine
- identifies the subroutine program
- first input instruction on first rung of subroutine
MCR
master control reset
clears all set non-retentive output rungs between paired MCR instructions
master control relay
- used in hardwired relay control circuitry to provide input/output power shutdown of entire circuit
- if its not energized there is no power flow to the load side of the MCR contacts
master control reset
- PLC version of master control relay
- if it is false, all nonretentive outputs are switched off
- used in pairs
- no address
start fence & end fence
- start fence: rung with a conditional MCR
- end fence: rung with an unconditional MCR
jump instructions
used to jump over instructions not pertinent to machine’s operation at that instant
label instruction
- target for jump instruction
- must have same address as jump instruction
timers
timers should be programmed outside the jumped section
subroutine
- short program used by main program to perform specific function
- placed in file number 3 through 255
