Modbus Communication Protocol; General - Teledyne 7500 Instruction Manual

5.

MODBUS COMMUNICATION PROTOCOL

5.1

General

The communication system by the MODBUS protocol is that the communication is always
started from the master station and a slave station responds to the received message.
Transmission procedures is as shown below.
1. The master station sends a command message to a slave station.
2. The slave station checks that the station No. in the received message matches with the
own station No. or not.
3. If matched, the slave station executes the command and sends back the response
message.
4. If mismatched, the slave station leaves the command message and wait for the next
command message.
a) In case when the station No. in the received command message matches with the
own slave station No.
b) In a case when the station No. in the received command message mismatches with
the own slave station No.
The master station can individually communicate with any one of slave stations connected on
the same line upon setting the station No. in the command message.
Teledyne Analytical Instruments
7