Modbus Operation - Siemens SEZ50MB Basic Documentation

Modbus Function Codes
Examples Of Using
Different Modbus
Function Codes
Function Code 0x01 à
Function Code 0x02 à
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Siemens
Building Technologies
4

Modbus Operation

The valid Function Codes are as follows:
Function Data
Functions
Code (Hex) Length
0x01 1 Read R/W Flag (Coil)
0x05 1 Write R/W Flag (Coil)
0x02 1 Read R-only Flag (Discrete Input)
0x03 2 Read R/W Register (Holding Register)
0x10 2 Write R/W Register
0x04 2 Read R-only Register (Input Register)
The following examples will illustrate how users can construct Modbus messages with
all available function codes above and the returned messages from the RWD via
SEZ50MB. (To interpret the meanings of the returned messages, please refer to the
next section RWD Parameters & Addresses).
Read RWD32S parameter (ADDR = 00001) called "bFrostEnable" with Modbus ADDR
= 0000:
SEZ50MB
Device
Address
Send F7
SEZ50MB
Device
Address
Respond F7
Read RWD68 parameter (ADDR = 10005) called "Q1_output" with Modbus ADDR =
0004:
SEZ50MB Function
Device Code
Address
Send F7 02
SEZ50MB Function
Device Code
Address
Respond F7 02
RWD Primary Controls Modbus Interface
Modbus Operation
Function Modbus Address
Code
01 00 00
Function Byte Status
Code Count
01 01 01
(bFrostEnable = Enable)
Modbus Address
00 04
Byte Status
Count
01 00
(Q1_output = Off)
RWD Parameter
Addressable
Ranges
0xxxx
e.g. 00001, 00003
1xxxx
e.g. 10004
4xxxx
e.g. 40109, 40111
3xxxx
e.g. 30001, 30007
Data Length CRC16
Check
00 01 E9 5C
CRC16
Check
A3 C0
Data Length CRC16
Check
00 01 EC 9D
CRC16
Check
92 00
CB1P3099en_01
27.10.2009