Allen-Bradley ProcessLogix 1756-IA16, Reference Manual, Page: 70 / 120

Publication 1757-RM810A-EN-P - May 2002
3-30 Functional Blocks
SR (Set dominant SR-FLIP-FLOP)
TRIG (Rising or Falling edge Trigger)
WATCHDOG
Description Provides a bistable Set Dominant flip-flop as defined in the IEC DIS 1131-3 standard.
Function Specifies the output (Q) of the flip-flop as a function of the input S (set), the input R (Reset), and the last state of Q.
Truth Table S
0 (OFF)
0 (OFF)
1 (ON)
1 (ON) R
0 (OFF)
1 (ON)
0 (OFF)
1 (ON) Q
No Change
0 (OFF)
1 (ON)
1 (ON)
Inputs S and R = Boolean values
Outputs Q = Boolean value controlled by the status of the input signals.
Parameters ORDERINCM
PVERSION Q
R S
Description Sets the output (OUT) to ON following the OFF-to-ON or ON-to-OFF transition of the input (IN) and stays at ON until
the next execution cycle, at which time it returns to OFF.
Function Provides edge change detection, thereby turning the output ON if an OFF-to-ON or ON-to-OFF transition is detected.
This block assumes that the input is starting at its OFF stage the first time it is activated.
Inputs IN = Boolean value
Outputs OUT = Boolean value
Parameters IN
ORDERINCM OUT
Description Monitors other system functions or remote devices and sets the output (OUT) to ON if the monitored function or
device fails.
Function
•
Used to monitor other system functions or remote devices.
•
Monitored function or device must set IN parameter to ON within a specified time interval (DELAYTIME),
otherwise it is assumed to have failed and output (OUT) is set to ON. The DELAYTIME is an integer with unit time
in seconds.
•
If output (OUT) is ON, it is reset to OFF as soon as IN is set to ON.
Inputs IN = Boolean value (ON/OFF)
Outputs OUT = Boolean value (ON/OFF)
Parameters DELAYTIME
IN ORDERINCM
OUT