<Toc> <Ind>
<7. I/O Communications >
7-5
IM 34M6H28-01E
1st Edition : Feb.01,1999-00
Store output data
Request to start scan
Confirm that
scanning is in progress
Access I/O data
Request to stop
scanning
Stop scanning
confirmation
Request to start/stop scanning
Scan status
Status of other
nodes
Input data buffer
Output data buffer
Scanning starts
Scan
(I/O
communications)
Scanning stops
CPU module
Operation from program
This module
Interface
Action
F0703.EPS
Figure 7.3 Operation Sequence and Operation of Module
■
Error processing during scanning
If an error occurs during I/O communications, two operation modes are provided as op-
tions, namely continue/ stop. During I/O communications, information possessed by the
slave may not be in agreement with the information of the scan list, or the stop/continue
operation can be specified when a slave is absent.
If "continue" is specified, communication continues with the slaves other than the one in
which the error has occurred. Communication automatically resumes when the slave in
which the error has occurred becomes available again. However, the red NS LED contin-
ues to blink until scanning stops (see Section 4.5, "Displays Panels," in this document.)
Slave operation when communication stops varies with the specifications of the slave.
Check the specification of the slave.
■
Ensuring data concurrency
I/O data are concurrent in every input/output data register (1 word). There are flags that
ensure data concurrency in all nodes when handling data that exceed 2 bytes, for instance,
when concurrency is required between NC data and data of a barcode reader or between
multiple data, etc. However, concurrency should be ensured when the slave transmits the
data.
• Input Data
Flags
•
Request to Prohibit Input Data Update flag in control flag of each node
•
Input Data Update Status flag in status flag of each node
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