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UDCNT2
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6.8 Other Convenient Instructions
6.8.2 Counter 2-phase input up or down (UDCNT2)
• The counter designated at is a ring counter. If it is counting up when the present value
is 32767, the present value will become 32768. Further, if it is counting down when the
present value is 32768, the present value will become 32767. The count processing
performed on the present value is as shown below:
(4) Count processing conducted according to the UDCNT2 instruction begins when the count
command goes from OFF to ON, and is suspended when it goes from ON to OFF.
When the execution command is turned OFF to ON again, the counting resumes from the
suspended value.
(5) The RST instruction clears the present value of the counter designated at and turns the
contact OFF.
1. With the UDCNT2 instruction, the argument device data is registered in the
work area of the CPU module and counting operation is processed as a system
interrupt. (The device data registered in the work area is cleared by turning the
execution command OFF, or turning the STOP/RUN switch STOP RUN.) For
this reason, the pulses that can be counted must have longer ON and OFF
times than the interrupt interval of the CPU module. The interrupt interval of
individual modules is shown below:
2. The set value cannot be changed during counting directed by the UDCNT2
instruction (while the execution command is ON). To change the set value, turn
OFF the execution command.
3. Counters designated by the UDCNT2 instruction cannot be used by any other
instruction. If they are used by other instructions, they will not be capable of
returning an accurate count.
4. The UDCNT2 instruction can be used as many as 5 times within all the
programs being executed. The sixth and the subsequent UDCNT2 instructions
are not processed.
Operation Error
(1) In the following case, an operation error occurs, the error flag (SM0) turns ON, and an error
code is stored into SD0.
• The device specified by exceeds the range of the corresponding device.
(Error code: 4101)
CPU Module Type Name Interrupt Interval
High Performance model QCPU, Process CPU,
Universal model QCPU
1 ms
D
32768 32767 2 1 0 1 2 3276732766
When counting down
When counting up
D
S