Yokogawa Data Acquisition with PID Control CX2000 - Manual (Page 28)

1-11
IM 04L31A01-17E
Functional Explanation
1
Modbus Slave
The CX can be connected as a Modbus slave device to a Modbus master device.
Modbus master devices (PLCs, PCs, etc.) can read and write to the internal register (D
register) of the CX.
To perform communications, the Modbus master device always sends a command
message to the CX first. A command message from the Modbus master includes
information such as the destination Modbus slave address (the address of serial
communication settings), the function code (operation command such as read and write),
and the register address.
When the CX receives the command message and the message contains no errors, the
CX operates according to the instruction and returns a message back to the Modbus
master device. If the command message contains errors, an appropriate error code is
returned to the Modbus master device.
Note
• The Modbus protocol has two signal transmission modes: RTU mode and ASCII mode. The
CX only supports the RTU mode.
• For details on the Modbus function codes that the CX supports, see section 4.5.
• For a description of the settings required in using this function, see section 4.2.
Load Data
Modbus master
Modbus slave device
Serial communications
CX
1.3 Serial Communication Function