Modbus Method - Omron RX Series User Manual

8 Communications Functions
8-2

Modbus Method

Communications Procedure
The inverter communicates with an external controller as follows.
(1) Query
External
controller
Inverter
(1) Frame (Query) that is sent from the external control device to the inverter
(2) After receiving a query frame, the inverter waits for the total time of the Silent Interval and the
Communication Wait Time (C078), before returning a response.
Silent Interval
The wait time that is specified on Modbus communication; its data length is 3.5 characters
(3.5 bytes).
It depends on the Modbus communication speed setting.
(3) Frame (Response) that is sent from the inverter back to the external controller
(4) After sending a response, the inverter monitors the time until it completes receiving the query frame
from the external control device. The inverter judges it as a communications error if it receives no
response within the Communication Error Timeout Time (C077).
Then, the inverter operates according the Operation Selection on Communication Error (C076),
while waiting for the reception of the first data again.
The monitoring of the Communication Error Timeout Time starts from the first sending/receiving
operation is established after the power supply is cycled or after the inverter is reset.
The inverter does not recognize as a communications error timeout if the sending/receiving
operation is not established at all.
For setting details, refer to the following information.
Parameter No.
C076
C077
C078
8 - 6
(3) Response
(2) Wait time (Silent interval + C078)
Function name
Operation Selection on
Communication Error
Communication Error
Timeout Time
Communication Wait Time
High-function General-purpose Inverter 3G3RX-V1 User's Manual (I578-E1)
(4) Communication Error Timeout (C077)
(Operates according to Operation Selection on
Communication Error (C076) when reception times out.)
Data
00: Trip (Trip after receiving timeout (E41))
01: Trip after deceleration stop (Deceleration
stop after receiving timeout, Trip after stop
(E41))
02: Ignore (No trip and no alarm output)
03: Free-run stop (Free-run stop after
receiving timeout. No trip and no alarm
output)
04: Deceleration stop (Deceleration stop after
receiving timeout. No trip and no alarm
output)
0.00: Function disabled
0.01 to 99.99: Length of time to occurrence of
a communications timeout
0. to 1000.: Wait time until response starts
after receiving is completed
(excluding silent interval)
(1) Query
Time
Default
data
02
0.00
0.
Unit
–
–
–