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Input processing
Before PLC executing the program, read every input terminal’s ON/OFF status to the image
area.
When the program is running, even the input changed, the content in the input image area will
not change until the next scanning period coming.
Output processing
After running all the instructions, transfer the ON/OFF status of output Y image area to the
output lock memory area. This will be the actual output of the PLC.
The output contactors will delay the action according to the output soft components reponse.
2-5 Auxiliary Relay (M, HM, SM)
The auxiliary relays in XD/XL series PLC are all in decimal form, please see the following
table:
In PLC, auxiliary relays are used frequently. This type of relay’s coil is same to the output
relay. They are driven by soft components in PLC;
Auxiliary relays M and HM have countless normally ON/OFF contactors. They can be used
freely, but this type of contactors can’t drive the external loads.
For common use
This type of auxiliary relays can be used only as normal auxiliary relays. I.e. if power supply
suddenly shut down during the running, the relays will be off.
Common usage relays can’t be used for power off retentive, but the zone can be modified;
For Power Off Retentive Use
The auxiliary relays for power off retentive usage, even the PLC is OFF, they can keep the
ON/OFF status.
Power off retentive zone cannot be modified;
Power off retentive relays are usually used to memory the status before stop the power, then
when power the PLC on again, the status can run again;
For Special Usage
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