
1.OVERVIEW OF PMC B-63983EN/02
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1.4.7 Notes on I/O Signals Updated by Other Than PMC
I/O signals transmitted over networks (such as an Ethernet, I/O Link-II,
PROFIBUS, DeviceNet, and FL-net) (signals assigned to addresses R,
D, and E) are updated asynchronously with PMC sequence program
execution.
Similarly, other applications (FOCAS2, C executor, real-time custom
macros, etc.) update I/O signals asynchronously with PMC sequence
program execution. Therefore, when a signal updated via a network or
by another application is to be used by a PMC sequence program, the
following should be noted:
(1) Note on input signals
When an input signal transmitted via a network or another
application is referenced at more than one place in the PMC
sequence program, the same value is not guaranteed to be
referenced within the same cycle of the sequence program.
To reference the same input signal value within the same cycle,
store the input signal status in an area such as an internal relay.
(2) Note on output signals
When an output signal is transmitted via a network or another
application, it may be transmitted to a slave unit in the middle of
the PMC sequence program execution cycle. Care should be
exercised when the slave unit references more than one signal.
(3) Note on multiple-byte data
When multiple-byte data is input or output via a network or
another application, concurrence of the data (a condition free
from data splitting) is not guaranteed. To ensure data concurrence,
perform handshaking, which does not cause data splitting during
data I/O.