GE 90-30/20/Micro DNCTR

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

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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.

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(enable) —>DNCTR|— (Q)

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(reset) —|R |

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(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.

RWhen 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.

QOutput Q is energized when the current value is less than or equal to zero.