Mitsubishi MELSEC-F User Manual page 83

5 COMMUNICATION PROCEDURE
Open completion signal
(BFM#20480)
5 - 9
1) Checking by KeepAlive
This method is used for a connection opened via the TCP/IP protocol.
The Ethernet module performs an existence check by sending an
existence check ACK message to a remote device with which
communication has not been performed for a certain period of time
and waiting to see whether or not a response is received. (
1 The connection is cut off if the remote device does not support the
TCP KeepAlive function (response to KeepAlive ACK messages).
2) Checking by PING
This method is used for a connection opened via the TCP/IP or
UDP/IP protocol.
The Ethernet module performs an existence check by sending a PING
command (using the ICMP echo request/response function) to a
remote device with which communication has not been performed for
a certain period of time and waiting to see whether or not a response
is received. (
2 Note that the Ethernet module automatically returns an echo
response packet when it receives a PING echo request
command. (It sends a response to the received PING command
even if the connection used in the data communication with the
remote device is closed.)
(b) The following actions are taken if a response message cannot be received
(an error is detected) from the remote device.
• The corresponding connection will be forcibly closed (the line is
disconnected). (
3 It is possible to reopen it with a user program.
• The open completion signal (the corresponding bit of BFM#20480) is
turned off and, the error code (C035
open error code storage area.
Also, the open/close status (BFM #1602 to 1609) value becomes
"0000 ".
H
Example: Assuming the values are set under the condition that the
Last
communication
Target
existence
check starting
interval timer
value
2
)
3
)
number of retries is three, the Ethernet module performs
target existence check at the timing shown in the figure below.
(An example of existence check by PING)
Ethernet module
PING PING
command command
(Retransmitted)
Target Target
existence existence
check interval check interval
timer value timer value
MELSEC-F
) is stored in places such as the
H
PING
command
(Retransmitted)
1
)
5 - 9