GE 90-30/20/Micro manual Dnctr

4

DNCTR

The Down Counter (DNCTR) function is used to count down from a preset value. The minimum preset value is zero; the maximum present value is +32,767 counts. The minimum current value is –32,768. When reset, the current value of the counter is set to the preset value PV. When the enable input transitions from OFF to ON, the current value is decremented by one. The output is ON whenever the current value is less than or equal to zero.

The current value of the DNCTR is retentive on power failure; no automatic initialization occurs at power-up.

_____

(enable)	(Q)
(reset) —R
(preset value) —PV

_____

		(address)
Parameters:
Parameter			Description
address	The DNCTR uses three consecutive words (registers) of %R memory to store the
	following:
	•	Current value (CV)= word 1.
	•	Preset value (PV)	= word 2.
	•	Control word	= word 3.
	When you enter an DNCTR, you must enter an address for the location of these
	three consecutive words (registers) directly below the graphic representing the
	function.
	Note: Do not use this address with another down counter, up counter, or any other
	instruction or improper operation will result.
	Caution: Overlapping references will result in erratic operation of the counter.
enable	On a positive transition of enable, the current value is decremented by one.
R	When R receives power flow, it resets the current value to the preset value.
PV	PV is the value to copy into the counter’s preset value when the counter is
	enabled or reset.
Q	Output Q is energized when the current value is less than or equal to zero.

4-22 Series 90-30/20/Micro Programmable Controllers Reference Manual–September 1998 GFK-0467K