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Class 1 and Class 2 polling

Class 2 is usually the regular polling path. Class 1 is the priority path for events, command confirmations, and pending urgent data.

What it means

Class 2 is usually the regular polling path. Class 1 is the priority path for events, command confirmations, and pending urgent data.

Class 2 requestUsed for regular low-priority data when no Class 1 demand is pending.

ACD=1 responseThe outstation tells the master that Class 1 data is waiting.

Class 1 requestThe master drains priority data until the pending condition clears.

Return to Class 2The master returns to regular polling after high-priority data is handled.

What to check in ARIEC60870

Use the software to connect the explanation to the frame evidence.

1A master that polls Class 1 continuously can starve regular traffic.

2Too much cyclic analog data configured as Class 1 can make commands feel slow.

3ARIEC60870 helps separate normal polling from a congested high-priority path.

TX10 49 01 4A 16request link status

RX10 0B 01 0C 16ACD=1, Class 1 waiting

TX10 7A 01 7B 16request Class 1 data

RX68 ... 16event or command confirmation

Protocol learning is easier when every concept is connected to a visible frame, counter, address, value, event, or report finding.