Instruction manual

7
(2) Reading (Address 1, Pattern 1, Step 1 step SV)
• Reading command from the master
(Fig. 5.5-3)
• Response from the slave in normal status [When SV=600
(0258H)]
(Fig. 5.5-4)
(3) Setting (Address 1, Pattern 1, Step 1 step SV) [When step SV is set to 600
(0258H)]
• Setting command from the master
(Fig. 5.5-5)
• Response from the slave in normal status
(Fig. 5.5-6)
6. Modbus protocol
6.1 Transmission mode
There are 2 transmission modes (ASCII and RTU) in Modbus protocol.
6.2 ASCII mode
Hexadecimal (0 to 9，A to F), which is divided into high order (4-bit) and low order (4-bit) out of
8-bit binary data in the command is transmitted as ASCII characters.
Data format Start bit : 1 bit
Data bit : 7 bits
Parity : Even/No/Odd (Selectable)
Stop bit : 1 bit/2 bits (Selectable)
Error detection : LRC (Longitudinal Redundancy Check)
Data interval : 1 second or less
(1) Message configuration
ASCII mode message is configured to start by [: (colon)(3AH)] and end by [CR (carriage return)
(0DH) + LF (Line feed)(0AH)]. (See Fig. 6.2-1)
(Fig. 6.2-1)
Slave address
Slave address is an individual instrument number on the slave side and is set within the range
00H to 5FH (0 to 95).
The master identifies slaves by the slave address of the requested message.
The slave informs the master which slave is responding to the master by placing its own address
in the response message.
[Slave address 00H (broadcast address) can identify all the slaves. However slaves do not respond.]
Slave
address
Function
code
Data
Error check
LRC
Delimiter
(CR)
Header
(:)
Delimiter
(LF)
(20H)
(44H 44H)
11 1
4
1
Command
type (20H)
Data item
Checksum
Header
(02H)
Sub
address
(20H)
Address
Delimiter
(03H)
21
Number of characters
(31H 31H 31H 30H)
(20H)
11 1
4
1
Command
type (20H)
Data item
Header
(06H)
Sub
address
(20H)
Address
4
Number of characters
1
Checksum
(30H 45H)
Delimiter
(03H)
2
Data
(31H 31H 31H 30H)
(30H 32H 35H 38H)
(20H)
11 1
4
1
Command
type (50H)
Data item
Header
(02H)
Sub
address
(20H)
Address
4
Number of characters
1
Checksum
(44H 45H)
Delimiter
(03H)
2
Data
(31H 31H 31H 30H)
(30H 32H 35H 38H)
(20H)
(45H 30H)
11
Checksum
Header
(06H)
Address
Delimiter
(03H)
21
Number of characters