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IEC-101 ACD and DFC

ACD tells the master that Class 1 data is waiting. DFC tells the master the outstation is not ready to receive more data.

What it means

ACD tells the master that Class 1 data is waiting. DFC tells the master the outstation is not ready to receive more data.

ACD=0No Class 1 data is currently requested by the outstation.

ACD=1Class 1 data is waiting. The master should request Class 1 before returning to normal polling.

DFC=0The outstation can accept data in the normal way.

DFC=1The outstation is busy or flow-controlled. Do not push more traffic blindly.

What to check in ARIEC60870

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

1Do not treat ACD as an alarm by itself. It is a scheduling clue for the master.

2Do not ignore DFC=1 during command tests; it can explain a slow or missing response.

3In ARIEC60870, check Frame Trace and Smart Findings when ACD or DFC keeps appearing.

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.