Rievtech PR-12 Series, User Manual And Programmers Manual

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5.4 Programming concepts
5.4.1 How the program works
The program is run by the loop, PLC reads and writes data continuously.When you
download the program to PLC and make PLC in the run mode, the PLC' s central
processing unit (CPU) executes the program in the following order:
A:PLC read input status.
B:The PLC program uses input values for logic control.
C:When the program is running and writes the results to the output image register.
D:At the end of the program, the output value of the output image register.
E: repeat the above steps.
PLC performs a series of tasks repeatedly. The cycle execution task is called the scan
cycle.PLC performs most or all of the following tasks during the scan cycle:
A: PLC read input status.
B:PLC executes the program's instructions, and stores the data in different memory
areas.
C: performs all communication requests.
D:PLC performs CPU self test diagnostic program.PLC ensure that the hardware,
program memory and all expansion modules are normal operation.
E:The values stored in the output image register are written to the actual output.
Attention: the execution of the scan cycle depends on the PLC that is set in the STOP
(stop) mode or the RUN (run) mode. In the RUN (run) mode, the program is executed;
in the STOP (stop) mode, the program is not executed.
5.4.2 Addressing overview
Identifying absolute and symbolic address
You can use absolute or symbol to identify the instructions in the program.Absolute
reference use memory area and bit or byte location to identify the address.symbolic
reference uses letters, numbers, and characters to identify addresses or values.
How to display the address of the program editor:
I0.0
The absolute address is made up of the memory area and the number