LSIS XBE-DC08A, Руководство пользователя, Страница: 1075 / 1284

Chapter 2 Built-in Cnet communication
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2) Frame structure in RTU mode
Frame structure in the RTU mode is as follows.
Classification Start
Station
number
Function code Data Error check End
size(byte) Idle time 1 1 N 2 Idle time
(1) Characteristic of RTU mode
a) It uses hexadecimal.
b) Start character is station number and frame is classified by CRC error check.
c) Start and end of frame is classified by adding idle time of 1 bit.
d) Between frames, there is interval of 3.5 character time. When exceeding 1.5 character time, it is acknowledged
as independent frame.
(2) Address area
a) It consists of 1 byte.
b) When using the XGT Cnet I/F module, range of station is 0~31.
c) Station number 0 is used for client.
d) When server responds, it contains self address to response frame to know client’s response.
(3) Data area
a) Transmits the data by using the Hex. data, data structure changes according to function code.
b) In case of receiving normal frame, it responds as normal response.
c) In case of receiving abnormal frame, it responds by using error code.
(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
is same with address 1 of data.
3) Expression of data and 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