7

FN8188.1

March 24, 2006

PIN DESCRIPTIONS

be applied independently or at the same time.)

fixed terminals of a mechanical potentiometer. The

of the terminal in relation to wiper movement direction

selected by the U/D input per potentiometer.

potentiometer which is equivalent to the movable terminal of

a mechanical potentiometer

Up/Down (U/D)

The U/D input controls the direction of a single

potentiometer’s wiper movement and whether the

counter is incremented or decremented.

Increment (INC)

The INC input is negative-edge triggered. Toggling INC

will move the wiper and either increment or decrement

the pertatining potentiometer’s counter in the direction

indicated

by

the

logic

level

on

the

pertaining

potentiometer’s U/D input.

Chip Select (CS)

A potentiometer is selected when the pertaining CS input

is LOW. Its current counter value is stored in nonvolatile

memory when the pertaining CS is returned HIGH while

the pertaining INC input is also HIGH. After the store

operation is complete the affected potentiometer will be

placed in the low power standby mode until the

potentiometer is selected once again.

PRINCIPLES OF OPERATION

There are multiple sections for each potentiometer in the

X93256: an input control, a counter and decode section;

the nonvolatile memory; and a resistor array. Each input

control section operates just like an up/down counter.

The output of this counter is decoded to turn on a single

electronic switch connecting a point on the resistor array

to the wiper output. Under the proper conditions the

contents of the counter can be stored in nonvolatile

memory and retained for future use. Each resistor array

is comprised of 31 individual resistors connected in

series. At either end of the array and between each

resistor is an electronic switch that transfers the

connection at that point to the wiper.

Each wiper, when at either fixed terminal, acts like its

mechanical equivalent and does not move beyond the

last position. That is, the counter does not wrap around

when clocked to either extreme.

If the wiper is moved several positions, multiple taps are

2-terminal resistance value for the device can temporarily

change by a significant amount if the wiper is moved

several positions.

When the device is powered-down, the last wiper

position stored will be maintained in the nonvolatile

memory for each potentiometer. When power is

restored, the contents of the memory are recalled and

each wiper is set to the value last stored.

X93256