LSIS XBE-DC08A, Руководство пользователя, Страница: 903 / 1284

Chapter 1 Built-in FEnet communication
1-24
Buil
t-
in
Comm
(2)
MBAP Header structure
Type Size Description Client Server
Transaction
Identifier
2byte
Separation of
MODBUS
request/response
processing
Initialized by the client
When the server
responds, it is copied
and responded.
Protocol
Identifier
2byte 0 = MODBUS protocol Initialized by the client
When the server
responds, it is copied
from the request frame.
2byte
Frame size except
MBAP Created by the client
(On request) Created by the server
(In case of response)
Unit Identifier 1byte
Separation of units
connected to the serial
line
Initialized by the client
When the server
responds, it is copied
from the request frame
(3)
Available function codes
Function codes Function Modbus transcription
Function Code 01 (h01) Reading output bit Read Coils
Function Code 02 (h02) Reading input bit Read Discrete Inputs
Function Code 03 (h03) Reading output word Read Holding Registers
Function Code 04 (h04) Reading input word Write Input Register
Function Code 05 (h05) Writing output bit Write single Coil
Function Code 15 (h0F)
Writing output bit
sequentially
Write Multiple Coils
Function Code 16 (h10)
Writing output word
sequentially
Write Multiple Registers
2) Frame structures by function codes
(1)
Function code h01 : Reading output bit (Read Coils)
• Request
Items Size Range
Function code 1 byte h01
Initial address 2 bytes h0000 ~ hFFFF
Number of coils 2 bytes h0001 ~ h07D0 (2000 bit)
• Response
Items Size Range
Function code 1 byte h01
Number of bytes 2 bytes N
Coil status n byte n = N or N + 1
• Error
Items Size Range
Function code 1 byte h81 (function code+ h80)
Exceptional code 1 byte h01,h02,h03,h04