Each time the input energy flow transitions from closed to open, the counter (CTUD) instruction determines the size of the current value compared to the set value. When the current value (CVxxx) is greater than (less than) the preset value (SV), the counter counts downwards (upwards). When the current value (CVxxx) is equal to the preset value (SV), the counter (Cxxx) is set to 1 and the current value (CVxxx) does not act. Performing a reset operation can reset the counter, that is, setting the counter bit (Cxxx) to 0 and resetting the preset value (SV).

Counter range: CVxxx=CV0 to CV255; Cxxx=C0 to C255.

Counter Type	Counter Bit Number	Maximum Value	Counter Number
CTUD	16 bits	32767	C0-C199
CTUD	32-bit	2147483647	C200 – C234
CTUD	32-bit (high-speed)	2147483647	C235-C255

Note: Since each counter has a current value, do not set the same counter number to more than one counter (up and down counters with the same number access the same current value)

Input/Output	Data Type	operand	Description
CV	16 bit integer	CV	Counter
SV	16 bit integer	D/CV/TV/AI/AO/K/H/V/Z/FD, bit composite word (X/Y/M/C/T/S), local variable (LW)	preset value

Command table:

NETWORK 000

LD X000

CTUD CV0 D0 // The counter determines the size relationship between CV0 and D0, and counts up and down from the current value CV0, with a set value (SV) of D0

NETWORK 001

LD C0

OUT Y000

图1 CTUD