Modbus Rtu Message Format; Broadcast Communication - Mitsubishi Electric MR-JE-C Series Instruction Manual

4. Modbus RTU

4.5 Modbus RTU Message Format

In the Modbus RTU communication, a command sent from a master (controller) to a slave (servo amplifier)
is called "Query Message", and a command that the slave (servo amplifier) returns to the master (controller)
is called "Response Message".
The servo amplifier that received a Query Message processes the command only after it passes through a
dataless section of 3.5 bytes or larger. The servo amplifier will send a Response Message to the controller
after the servo amplifier's response time has passed. When the controller sent a Query Message without
securing a dataless section of 3.5 bytes or larger, the servo amplifier does not respond. Execute processing
so that the controller sends the next Query Message only after it receives a Response Message sent from
the servo amplifier.
Query Message
Master (controller)
Slave (servo amplifier)
Note. The servo amplifier response time differs depending on the command to send.

4.6 Broadcast Communication

The Modbus RTU communication supports the broadcast communication in which a Query Message is sent
from the master (controller) to all slaves (all axes of servo amplifiers). In this case, the servo amplifiers do
not return a Response Message. Execute processing so that the master sends the next Query Message
after the slave processing time has passed. The broadcast communication supports only the function code:
"10h" (Preset Multiple Registers).
Query Message
Master (controller)
Slave (servo amplifier)
Note. The waiting period before sending Query Message varies depending on a command to be sent. Refer to the following table.
For writing data of 4 bytes
For writing data of 244 bytes
Dataless section (3.5 bytes or larger)
Servo amplifier response time (Note)
Dataless section (3.5 bytes or larger)
Waiting period before sending Query Message (Note)
Condition
Response Message
No. of Registers
(Number of registers to write)
2
122
4 - 4
Query Message
Query Message
Waiting time for sending
query message
24 [ms]
300 [ms]