Counter instructions
702
Part III FP Instructions
CT_FB
Down Counter
For the CT_FB function block declare the following:
Count count contact
each time a rising edge is detected at Count, the value 1 is subtracted from the elapsed value EV
until the value 0 is reached
Reset reset contact
each time a rising edge is detected at Reset, the value 0 is assigned to EV and the signal output C
is reset; each time a falling edge is detected at Reset, the value at SV is assigned to EV
SV set value
value of EV after a reset procedure
C signal output
is set when EV becomes 0
EV elapsed value
current counter value
PLC types Availability of CT_FB (see page 1319)
Variable Data type Function
Count count contact (down)
Reset
BOOL
reset contact
SV INT set value
C BOOL set when EV = 0
EV INT elapsed value
Time chart
Count
Reset
SV
EV
C
10
0
10
0
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PROG mode
ON
OFF
RUN mode
ON
OFF
ON
OFF
Description
Counters realized with the CT_FB function block are down counters. The count area SV (set value)
is 1 to 32767.
Data types
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