Hitachi SJ-P1 Series - Data Formats

7-3
Chapter 7
About the Modbus TCP
7.2.3 Data format
The data formats of MBAP Header and PDU are
shown below
■Data format of MBAP Header
*1) In case configuring a length setting which
differs from the specification, it will be
determined as the error and there will be no
response.
■Data format of PDU
The transfer from client (higher-level device) to the
server (P1-EN) and server (P1-EN) to client
(higher-level device) have the same format.
Address
Items
Description
0,1
Transaction Identifier
The client (higher-level device) to the server (P1-EN):
Configure an arbitrary ID to identify the transaction.
The server (P1-EN) to the client (higher-level device):
It returns the received data as it is.
2,3
Protocol Identifier
The client (higher-level device) to the server (P1-EN):
Configure "0000h".
The server (P1-EN) to the client (higher-level device):
It returns "0000h".
4,5
Length
Configure the size of datas united Unit ID (address 6) and PDU
(address 7 to N). (unit: the number of bytes) *1)
6
Unit Identifier
The client (higher-level device) to the server (P1-EN):
Configure "FFh".
The server (P1-EN) to the client (higher-level device):
It returns "FFh".
Address
Items
Description
7
Modbus function code
The client (higher-level device) to the server (P1-EN):
Configure an arbitrary Modbus function code.
The server (P1-EN) to the client (higher-level device):
In the case of normal response, it returns the Modbus function
code.
Or in the case of exception response, it returns the code the
Modbus function code concatenated with "80h".
8～N
Data
The client (higher-level device) to the server (P1-EN):
Configure the inquiry data.
The server (P1-EN) to the client (higher-level device):
It returns the response data.
Or in the case of exception response, it returns the exception
code.