
B-63983EN/02 1.OVERVIEW OF PMC
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Notes on programming asynchronous I/O signals
Normal input signals from the CNC are transferred to the PMC at
intervals of 4 or 8 msec. Normal output signals to the CNC are
transferred from the PMC at intervals of 4 or 8 msec. Therefore, I/O
signals exchanged with the CNC are usually transferred at intervals of
4 or 8 msec. When creating a sequence program, note that the input
signals from the CNC are not synchronized with the 1st and 3rd level
sequence program parts. Because the input signals from the CNC are
asynchronous, the status of an input signal from the CNC may change
during execution of the 1st level sequence program part, which can lead
to a problem as shown in Fig. 1.4.5 (b). To prevent such a problem,
write the TF signal to an internal relay at the beginning of the 1st level
sequence part so that the subsequent operation of the 1st level sequence
program part references the internal relay. Then, the TF signal can be
treated as a synchronous signal. See Fig. 1.4.5 (c).
Signals input from the machine via the I/O Link and signals input from
other control units over a network are also asynchronous, so these
signals should be treated in a similar manner.
If the TF status changes to 1 after TF=0 is read first,
W1 and W2 may be set to 1 momentarily.
Fig. 1.4.5 (b)
When the TF signal is made synchronized, neither W1
nor W2 is set to 1.
Fig. 1.4.5 (c)