Yokogawa Button Operated MV2000 - Manual (Page 166)

App-2 M-4662
Appendix 2 Data Dropout during Modbus
Communication
Data Dropout When Operating as a Modbus Client
If the MV tries to issue a command to a server device but has not finished receiving
a response to the previous command, the MV will not be able to transmit the next
command. This will cause a data dropout. Take appropriate measures to prevent
dropouts by referring to the following figures.
Read cycle
Data dropout
(Servers 2 and 3)
Data dropout
(Server 3)
Server device 1
Server device 2
Server device 3
G
G
G
G
G
G
Read cycle
(Retry)
: Status lamp
: Response from the server device
: Command from the MV
Data dropout
(Servers 2 and 3)
Server device 1
Server device 2
Server device 3
Read cycle
Timeout value
Connection dropped
Data dropout
(Servers 2 and 3)
Server device 1
Server device 2
Server device 3
G G
G
G
G
G G
O
Connection dropped Connection recovered
Timeout value
G
G
G
G
O
Y
Connection retry time*
G G
G G G
G
Y
O R
1. When the response from the server device takes a long time
2. When the connection is dropped because there is no response from the server device
3. When the communication recovers through connection retry
* The first connection retry after the connection is
dropped is shorter than the specified interval. The
status lamp indications in this example apply
when the connection retry function is enabled.