MODBUS communication function
5-1 HECR
5 MODBUS communication function
MODBUS protocol is a communication protocol developed by Modicon. It is used to communicate with a PC
or PLC.
Register content is read and written by this communication protocol.
This communication has the following features.
• Control run/stop.
• Set temperature and read.
• Read the internal sensor.
• Read the external sensor.
• Read the condition of the product.
• Read the alarm generating condition of the product.
• Read and set the control parameter(PID values).
Refer to “5.10 Register Map” for the register of the product.
5.1 Precautions for communication
5.1.1 Precautions after wiring and before communication
1) Check or set the each communication setting by the operation display panel.
• The communication specification shall be the customer’s communication standard
(RS-485 or RS-232C).
• The serial protocol shall be the MODBUS.
• The communication mode shall be the SeriRem (Serial remote mode).
Other modes can perform reading, but only SERIAL mode can perform writing.
2) Check or set the communication parameters using the operation display panel.
Check or set the communication speed so that the product synchronizes with the host
computer (master) prepared by the customer.
3) Check the slave address (unit number) by the operation display panel.
No response is returned when a request message is sent from a slave address other
than those set in the product.
5.1.2 Precautions for communicating
1) Allow a suitable interval between requests.
To send request messages in series, wait for 50 msec. or longer after receiving a
response message from the product before sending the next message.
2) Retry (resend request message).
The response may not be returned due to noise. If no message is returned 3sec. after
sending a request message, resend the request message.
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