Operation Processing Method Of The Plc Function - Mitsubishi Electric A800 Programming Manual

Operation processing method of the PLC function

3.5
Operation processing method of the PLC
function
The PLC function uses the repetitive operation method of stored programs.
Stored program method
• The stored program method stores a sequence program to be operated in the internal memory in advance.
• At execution of the sequence program, the sequence program stored in the PLC function is read to the CPU by each
instruction in order to execute operations, and that result is used to control each device status.
Repetitive operation method
The repetitive operation method executes a sequence of operations repeatedly.
The PLC function executes the following process repeatedly.
• The PLC function executes a sequence program stored in the internal memory in sequence from step 0.
• The PLC function performs internal processing such as updating timers/counters to the present values and performing
self-diagnostic checks after executing the END instruction, and returns to step 0 in the sequence program.
NOTE
• Processing from step 0 to the next step 0 or END to the next END is called a scan.
Therefore, a single scan time is the total time to process a user-created program (step 0 through END) and the time for
internal processing of the PLC function.
78
Sequence program
Step 0
Step 1
Step 2
Built-in sequence function repeats
this operation.
END
·Timer/counter present
value updating
·Self-diagnostic
checks, etc.