User manual
Modbus RTU 13MN744
Inputs (Modbus 3xxxx Reference Set)
Analog inputs are mapped to Modbus Inputs for H2.
Read Input Registers (Function Code 04)
This function code is used to read from 1 to approx. 125 contiguous input registers in a remote device. The
Request PDU specifies the starting register address and the number of registers. Registers are addressed
starting at zero. Therefore, input registers 1-16 are addressed as 0-15.
The register data in the response message are packed as two bytes per register, with the binary contents right
justified within each byte.
For each register, the first byte contains the high order bits and the second contains the low order bits.
Request PDU
Function Code 1 Byte 0x04
Starting Address 2 Bytes 0x0000 to 0xFFFF
Quantity of Inputs 2 Bytes 0x0001 to 0x7D0
Response PDU
Function Code 1 Byte 0x04
Byte Count 1 Byte 2xN*
Input Status N* x 2 Bytes
*N = Quantity of Input Registers
Error
Error Code 1 Bytes 0x84
Exception Code 1 Bytes 01 or 02 or 03 or 04
Example of a request to read input register 9:
Request Response
Field Name (Hex) Field Name (Hex)
Function 04 Function 04
Starting Address Hi 00 Byte Count 02
Starting Address Low 08 Input Reg 9 Hi 00
Quantity of Input Reg Hi 00 Input Reg 9 Lo 0A
Quantity of Input Reg Lo 01
Table 8 Input Table
Modbus Ref Inputs
Location Description
30001L Control Card Analog Input 1 - ±100% IEEE floating point
30002H Control Card Analog Input 1 - ±100% IEEE floating point
30003L Control Card Analog Input 2 - ±100% IEEE floating point
30004H Control Card Analog Input 2 - ±100% IEEE floating point
30005L Option Card 1 Analog Input 3 - ±100% IEEE floating point
30006H Option Card 1 Analog Input 3 - ±100% IEEE floating point
30007L Option Card 1 Analog Input 4 - ±100% IEEE floating point
30008H Option Card 1 Analog Input 4 - ±100% IEEE floating point
30009L Option Card 2 Analog Input 5 - ±100% IEEE floating point
30010H Option Card 2 Analog Input 5 - ±100% IEEE floating point
30011L Option Card 2 Analog Input 6 - ±100% IEEE floating point
30012H Option Card 2 Analog Input 6 - ±100% IEEE floating point