7 Serial Communications
7 - 30
NX-series Communications Interface Units User’s Manual (W540)
7-7 User Programming to Restart a Port
If the system configuration does not allow you to use serial communications instructions for CIF Units,
you must program processing for the serial communications protocol in the user program.
This section describes the processing that is performe
d to restart a port in the user program.
Precautions for Correct Use
Refer to 1-4-2 Conditions for Using Serial Communications Instructions for CIF Units on page
1-8 for detailed conditions on using the serial co
mmunications instructions for CIF Units.
The CPU Unit or communications master and CIF Unit exchange input notification data and output noti-
fication data in each I/O refresh cycle. The Input SID in the inp
ut notification data and the Output SID in
the output notification data must match. Refer to 7-3-2 SIDs and SID Responses on
page 7-7 for
detailed specifications for the Input SID and Output SID.
If the values of the Input SID and Output SID do no
t match, the port on the CIF Unit must be restarted
to initialize the values so that they match again. Place processing to restart the CIF Unit port in the user
programming that is executed in the CPU Unit or communications master.
The values for the Input SID and Output SID may beco
m
e mismatched in the following cases.
• A power interruption occurs only in th
e CPU Unit or communications master.
• A power interruption occurs only in the Slave Te
rminal or CIF Unit.
• A communications network error occurs and is then reset.
For a programming sample for rest
arting
a port, refer to A-4-2 Programming Sample 1: Restarting CIF
Unit Ports on
page A-32.
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