LSIS XGL-C22A, User Manual, Page: 153 / 299

Chapter 8 Modbus Communication
8-4
(4) Error check area
It determines if frame is normal or not by using CRC check of 2 byte.
(5) Modbus address regulation
Address in the data starts from 0 and it is same with value that is minus 1 from modbus memory, Modbus
address 2 is same with address 1 of data.
8.3.3 Data and expression of address
To express data and address of modbus protocol, the characteristic is as follows.
(1) It used hexadecimal as basic form.
(2) In the ASCII mode, Hex data is converted into ASCII code.
(3) RTU mode uses Hex data.
(4) Each function code has following meaning.
Code(Hex) Purpose Used area address Max. response data
01
Read Coil Status
Bit output 0XXXX 2000bit
02
Read Input Status
Bit input 1XXXX 2000bit
03
Read Holding Registers
Word output 4XXXX 125word
04
Read Input Registers
Word input 3XXXX 125word
05
Force Single Coil
Bit output 0XXXX 1bit
06
Preset Single Register
Word output 4XXXX 1word
0F
Force Multiple Coils
Bit output 0XXXX 1968bit
10
Preset Multiple Registers
Word output 4XXXX 120word
8.3.4 Reading data of bit type at the bit output (01)
(1) Reading bit of output area (function code: 01)
In case of reading data of bit type, request and response frame is as follows.
Detail of frame is applied in case of ASCII mode.
(a) Request frame
Frame
Station
no.
Function code
(01)
Address Data size
Frame error
check
Tail (CRLF)
Size (byte) 1 1 2 2 2 2
(b) Response frame (In case of receiving normal frame)
Frame
Station
no.
Function code
(01)
No. of byte Data Frame error check Tail (CRLF)
Size (byte) 1 1 2 N 2 2