GE VersaPoint IC220PBI002, Руководство пользователя

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8-8 VersaPoint™ I/O System Profibus-DP NIU User’s Manual – August 2005 GFK-1911B
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<Length of PCP data>
Specifies how many bytes of PCP object data (object contents) follow.
<PCP object data>
The actual contents of a PCP object.
<PCP acknowledgment>
The structure of a PCP acknowledgment is:
<Message code> <Result> <Length of PCP data> <PCP object data> or
<Message code> <Result> <PCP error code>
<Invoke ID>
The Invoke ID is one byte in length and is used for channel selection on some
modules.
The message code is 81
hex
(PCP Read) or 82
hex
(PCP Write). The result has the
function of a status byte (0 means "OK", 44
hex
means "general error"). "Length of
PCP data" and "PCP object data" only contain specific values on a read response
(Read). "Length of PCP data" specifies how many bytes of PCP object data
(object contents) follow. The "PCP object data" contains the actual contents of a
PCP object. In the event of an error, the status byte is directly followed by the PCP
error code.
When accessing PCP, the first byte in the DP/V1 data block uses PCP Read (= 01
hex
) and PCP Write (= 02
hex
) to indicate whether the PCP object should be read
or written.