Modbus Functions; 03) Read Holding Register - Fronius Ri Fb Inside/I Bedienungsanleitung

Modbus Functions

03 (03 ) This code is used to read the contents of a contiguous block of holding registers
dec hex
in a remote device. In the "Special Data" area, this contiguous block is limited to
Read Holding
1-4 registers. The request PDU determines the starting register address and the
Register
number of registers.
The registers are addressed in the PDU starting at zero. This means registers
numbered 1-16 will be addressed using 0-15.
The register data in the response message is packed as two bytes per register,
with the binary contents precisely aligned/justified within each byte. Within the
individual registers, the first byte contains the high-order bits and the second
byte the low-order bits.
Request
Function code
Starting address
Number of registers
Response
Function code
Number of bytes
Register value
N* = number of registers
Error
Error code
Exception code
Example
Example read request for register E011
Request
Field Name
Transaction Identifier Hi
Transaction Identifier Lo
Protocol Identifier Hi
Protocol Identifier Lo
Length Hi
Length Lo
Unit Identifier
Function code
Starting Address Hi
Starting Address Lo
No. of Registers Hi
68
1 byte 03
hex
2 bytes 0000
hex
2 bytes 1 to 125 (7D
1 byte 03
hex
2 bytes 2 x N*
N* x 2 bytes -
1 byte 83
hex
1 byte 01 or 02 or 03 or 04
(gas pre-flow).
hex
Response
Hex Field Name
00 Transaction Identifier Hi
01 Transaction Identifier Lo
00 Protocol Identifier Hi
00 Protocol Identifier Lo
00 Length Hi
06 Length Lo
00 Unit Identifier
03 Function code
00 Byte Count
11 Register value Hi (108)
00 Register value Lo (108)
to FFFF
hex
)
hex
Hex
00
01
00
00
00
05
00
03
02
08
98