Operating Instructions

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Siemens Engineering Guide SOC7-128 Modbus interface SE1Z5996en7
Building Technologies 4 Register map and function codes 2015-08-26
4 Register map and function codes
4.1 Register map
Modbus registers are organized into reference types identified by the leading number of
the reference address:
The "x" following the leading character represents a four-digit reference address.
ModbusType Reference Description (refer to a Master device)
Coil Status 0xxxx
Read/Write Discrete Outputs or Coils.
A 0x reference address is used to drive output data
to a digital 1-bit output channel.
Input Status 1xxxx
Read Discrete Inputs.
The 1-bit status of a 1x reference address is
controlled by the corresponding digital input channel.
Input Register 3xxxx
Read Input Registers.
A 3x reference register contains a 16-bit number
received from an external source—e.g. an analog
signal.
Holding
Register
4xxxx
Read/Write Output or Holding Registers.
A 4x register is used to store 16-bits of numerical
data (binary or decimal), or to send the data from the
CPU to an output channel.
The leading character is generally implied by the function code and omitted from the
address specified for a given function. The leading character also identifies the I/O
data type.
4.2 Function codes
The functions below are used to access the registers outlined in the register map of the
module for sending and receiving data.
Function
Code
Modbus function Modbus master application
01
Read Coil Status Read multiple DOs (0xAdr)
02 Read Input Status
Read multiple DIs (1xAdr)
03
Read Holding Registers Read multiple AOs (4xAdr)
04 Read Input Registers
Read multiple AIs (3xAdr)
05
Force Single Coil Write single DO (0xAdr)
06
Preset Single Register Write single AO (4xAdr)
15
Force Multiple Coils Write multiple DOs (0xAdr)
16
Preset Multiple Registers Write multiple AOs (4xAdr)
When the slave device responds to the master, it uses the function code field to
indicate either a normal (error-free) response, or that some kind of error has occurred
(an exception response).
Modbus Data formats
Supported
Modbus commands