Cutler-Hammer D320 PLC, User Manual

Page: 161 / 258

Chapter 6: Instructions
149
Instruction
Mnemonic Constant Cycle Interrupt
Routine
Range
Bit
Word
INT
RETI INT: Start of constant cycle
routine
RETI: End of constant cycle
routine
Double words
Ladder
INT: Begin block of constant cycle scan instructions.
Ni: The constant cycle interrupt time interval.
Range: 1 to 999 (20 ms to 10 sec)
Time interval: (Ni + 1)
×
10 msec
RETI: End block of constant cycle scan instructions.
Description
1. The INT/RETI instructions are used to mark a block of instructions that are to be executed on
a constant time cycle, asynchronous with the scan time of the PLC.
2. The time interval of the constant cycle routine can be set from a minimum of 20 msec to a
maximum of 10 sec. The constant cycle time is indicated by the Ni parameter. The time
calculation is (Ni+1)
×
10 msec.
3. The constant cycle routine is controlled by the F0.11 contact. If the F0.11 contact is On, the
constant cycle routine is executed. If it is Off, the constant cycle routine block is ignored.
4. Only one constant cycle routine can be made within a program.
5. The time required to execute the constant cycle routine instructions MUST be less than the
overall scan time of the main program. If the execution time of the constant cycle routine is
greater than the overall scan time, the program will not operate properly. For this reason, the
constant cycle routine should be limited to a minimum number of steps.
Example
Program Expression Operation Results
If the R0.0 input is On, the constant cycle interrupt
routine will be executed. Instructions between
INT/RETI shall be executed on a constant time base
of (9+1)
×
10 msec = 100 msec. The constant cycle
interrupt is controlled in the main program using the
R0.0 contact.
F0.11 is the system flag that controls the execution of
the INT routine.
INT
Ni =
RETI
F0.11
(OUT)
R0.0
INT
Ni = 9
RETI
If R0 is On, perform
constant cycle interrupt
routine every 100 msec.