User manual

5 Universal (General-purpose communication)
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5.4.3 Communication frame organization
5.4.3.1 Query master part
Station Function code Data area
CRC
L H
① ② ③ ④
Item
Description
①Station
It is slave station (HEX) receiving a message from master. Setting range is
0 to 255. If it is 0, it is broadcast query which sends message to every
slave.
②Function code (HEX)
Slave executes designated function according to function code. Available
set code is 01(Read Coils), 15(Force Multiple Coils), 03(Read Holding
Register) and 16(Force Multiple Register).
③Data area (HEX)
Transmit data related with function code. Data organization consists of
(Upper 1byte) + (Lower 1byte) of the appropriate address. The length of
area is variable and it is able to communicate without data.
④CRC(HEX)
It is error check area. It calculates using CRC-16 code.
It consists of 2btye. (Lower 1byte of CRC) + (Upper 1byte of CRC)
(1) Read Coils(Func01-01H)
Slave
Address
(station)
Function
(command)
Starting Address
(starting address)
No. of Points
(the number of data)
Error Check
(CRC16)
Hi(upper) Lo(lower) Hi(upper) Lo(lower) Lo(lower) Hi(upper)
1Byte 1Byte 1Byte 1Byte
1Byte 1Byte 1Byte 1Byte
(2) Force Multiple Coils(Func15-0FH)
Slave
Address
(station)
Function
(command)
Starting Address
(starting address)
No. of Coils
(the number of data)
Byte Count
(the number of data
byte)
Hi(upper) Lo(lower) Hi(upper) Lo(lower)
1Byte 1Byte 1Byte 1Byte 1Byte 1Byte 1Byte
Data
(data)
Data
(data)
Data
(data)
Data
(data)
Error Check
(CRC16)
Lo(lower) Hi(upper)
1Byte 1Byte 1Byte 1Byte 1Byte 1Byte
(3) Read Holding Registers(Func03-03H)
Slave
Address
(station)
Function
(command)
Starting Address
(starting address)
No. of Points
(the number of data)
Error Check
(CRC16)
Hi(upper) Lo(lower) Hi(upper) Lo(lower) Lo(lower) Hi(upper)
1Byte 1Byte 1Byte 1Byte
1Byte 1Byte 1Byte 1Byte