Mitsubishi Electric QJ71E71-100 User Manual page 218

*1 The following shows the timing of issuing the system switching request.
• System switching timing when an alive check is used
Open completion signal
(address: 5000
The last communications
• System switching timing when a ULP timeout is used
BUFSND instruction
BUFSND instruction
completion device + 1
*2 Set whether to issue the system switching request in the redundant settings of the programming tool. (
Section 14.7.3)
216
When the E71 has not communicated with the connected device where a connection is open for a certain
period of time, it performs an alive check. If the E71 cannot receive a response message from the
connected device, it closes the corresponding connection and issues a system switching request to the
control system CPU module. (The following figure shows an example where an alive check message is
resent twice.)
)
H
A response message cannot be received from
the connected device.
E71
Destination existence
confirmation starting
interval timer value
If ACK is not returned from the connected device within the TCP ULP timer time when the connection is
open in TCP/IP or data is sent, a sending error occurs and the E71 issues a system switching request to
the control system CPU module. (The following figure shows an example where the number of retries is set
twice.)
E71
Data
command
TCP resend
timer value
Alive check Alive check
resent
(1st time)
Destination
Destination
existence
existence
confirmation
confirmation
interval timer
interval timer
ACK is not returned from
the connected device.
1st retry 2nd retry
TCP resend TCP resend
timer value timer value
TCP ULP timer value
Alive check
resent
(2nd time)
Destination
existence
A request for system switching
confirmation
to the control system CPU
interval timer
module is issued.
A request for system
switching to the control
system CPU is issued.
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