Chapter 4. Ladder Diagram (LD) Programming
GFK-2950C February 2018 135
4.7.2 Down Counter
The Down Counter (DNCTR) function counts down from a preset value. The minimum
Preset Value (PV) is zero; the maximum PV is +32,767 counts. When the Current Value
(CV) reaches the minimum value, -32,768, it stays there until reset. When DNCTR is reset,
CV is set to PV. When the power flow input transitions from OFF to ON, CV is
decremented by one. The output is ON whenever CV ï‚£ 0.
The output state of DNCTR is retentive on power failure; no automatic initialization occurs
at power-up.
Warning
Do not use the Address of the down counter with other
instructions. Overlapping references cause erratic
counter operation.
Note: For DNCTR to function properly, you must provide an initial reset to set the CV to the value in
PV. If DNCTR is not initially reset, CV will decrement from 0 and the output of DNCTR will be
set to ON immediately.
Operands
The beginning address of a three-word WORD array:
Word 1: Current Value (CV)
Word 2: Preset Value (PV)%
Word 3: Control word
When R receives power flow, it resets the counter's CV to PV.
Preset Value to copy into word 2 of the counter's address
when the counter is enabled or reset. 0 ï‚£PV ï‚£ 32,767. If PV is
out of range, word 2 cannot be reset.
The current value of the counter
All except S, SA, SB, SC
and constant
Example – Down Counter
DNCTR counts 5000 new parts before energizing output %Q00005.
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