Mitsubishi MELSEC-F User Manual page 82

5 COMMUNICATION PROCEDURE
Transmission request
and status
#1610 to 1617
5 - 8
(3) When communication errors occur, the setting value should be changed to
increase the number of retries.
The number of retries is obtained by using the following equation:
(In case of the default values, 2 = (60/20) - 1)
Number
•
of retries
Example: Assuming the values are set in such a way that the number of retries is
two, a data transmission error will occur at the timing shown in the figure
below if data transmission fails (when communicating using fixed buffer).
W
0001H
Data
command
A : TCP resend timer value
(The time after which the data should be retransmitted when
an "ACK" is not returned after sending data.)
(4) Perform the following setting in order to eliminate the retries explained in (3) (i.e.,
to set the number of retries to 0).
TCP ULP
•
=
timer value
(Each timer value should be identical.)
(5) The target existence check is a function whereby the Ethernet module checks
whether or not a remote device is functioning normally by sending an existence
check message and then waiting to see whether a response message is
received. It is used if a connection to a remote device is open but
communication with the remote device has not been performed for a certain
period of time.
(a) The existence check function has two methods of checking: PING and
KeepAlive.
The Ethernet module performs each of the existence checks based on the
setting values explained in (7) to (9) of this section and the existence
check setting of the open settings (refer to Section 5.5 (6)).
The existence check function (Ping or KeepAlive) can be selected at the
time of operation setting or re-initialization.
For the operation setting, refer to Section 4.6.
Refer to Section 5.2.3 for the explanation on re-initialization.
TCP ULP timer value
-1
TCP resend timer value
R
0002H
Ethernet module
First retry
A A
TCP ULP timeout value
TCP end
TCP resend
=
timer value
timer value
MELSEC-F
R
0008H
Second retry
A
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