Quantum Ethernet TCP/IP Modbus Application Protocol
The header is 7 bytes long, and includes the following fields:
inv_id[2 bytes] invocation id used for transaction pairing
proto_id[2 bytes] used for
len[2 bytes] the len field is a byte count of the remaining fields and includes the dst_id and data fields.
The remainder of the pdu includes two fields:
dst_idx[1 byte] destination index is used for
data[n bytes] this is the service portion of the Modbus pdu, mb_pdu, and is defined below
The service portion of the Modbus Application Protocol, called mb_pdu, contains 2 fields:
mb_pdu ::= { func_code[1], data[n] }
func_code[1 byte] MB function code
data[n bytes] this field is function code dependent and usually contains information such as variable references, variable counts, and data offsets.
The size and content of the data field are dependent on the value of the function code.
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