Yokogawa Data Acquisition with PID Control CX2000 - Manual (Page 109)

4-15
IM 04L31A01-17E
4
Modbus Protocol
• Response
Slave
address Function
code Byte
counter Register
content
(Low) Register
content
(High) Register
content
(Low) Error
check Register
content
(High)
• • • •
Write to Multiple Hold Registers (Function Code 16)
Writes the specified number of points of data consecutively to the registers from the specified
register number. The maximum number of points that can be written at once is 100.
Broadcast request (setting the slave address to 00) is possible.
• Command message
Slave
address Function
code Register start
number
(High) Register start
number
(Low) Number of
registers
(High) Number of
registers
(Low) Error
check Byte
counter Data
(High) Data
(Low) • • • •
• Response
Slave
address Function
code Register start
number
(High) Register start
number
(Low) Number of
registers
(High) Number of
registers
(Low) Error
check
Write to Single Hold Register (Function Code 6)
Writes the data to the specified number. Only a single data point is written at once.
Broadcast request (setting the slave address to 00) is possible.
• Command message
Slave
address Function
code Number of
registers
(High) Number of
registers
(Low) Error
check Written data
(High) Written data
(Low)
• Response
Slave
address Function
code Number of
registers
(High) Number of
registers
(Low) Error
check Written data
(High) Written data
(Low)
Loopback Test (Function Code 8)
This command is used to check the connection.
An arbitrary value can be selected for the transmitted data, and the same value is
returned as a response.
• Command message
Slave
address Function
code 00
(High) 00
(Low) Error
check Transmitted
data
(High) Transmitted
data
(Low)
• Response
Slave
address Function
code 00
(High) 00
(Low) Error
check Same as
transmitted data
(High) Same as
transmitted data
(Low)
4.5 Communications as a Modbus Slave