Mitsubishi Electric MELSECQ Series User Manual page 77

5
FUNCTIONS
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POINT
When reading a periodic pulse count value with the sequence program, use either
of the following methods.
(1) Read a data block of six words from the previous periodic pulse count value
(Un\G14 and 15) using the DFRO instruction, and check that the previous
periodic pulse count value (Un\G14 and 15) is equal to the judgment value for
updated periodic pulse count value (Un\G18 and 19). If not equal, try reading
again.
The following example program reads the periodic pulse count value of
channel 1 of the QD63P6 that is mounted in the slot position of I/O number X/
Y00 to X/Y1F when M0 is turned ON.
Figure 5.13 Periodic pulse counter value reading program example
(2) Use the dedicated instruction, G(P).PPCVRD . (Refer to Appendix 1.2.)
When the periodic pulse count value is read with the G(P).PPCVRD
instruction, the determination on consistency in the sequence program is
unnecessary.
If either of the above methods is not used, the previous and present values may
be the same due to the update timing of the module and reading timing of the
sequence program, and may cause inconsistency in the periodic pulse count
values.
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5.5 Using the Periodic Pulse Counter Function
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