6

FN8188.2

February 1, 2008

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.

Instructions and Programming

The INC, U/D and CS inputs control the movement of the

pertaining wiper along the resistor array. With CS set LOW

the pertaining potentiometer is selected and enabled to

respond to the U/D and INC inputs. HIGH to LOW transitions

on INC will increment or decrement (depending on the state

of the U/D input) a 5-bit counter. The output of this counter is

decoded to select one of thirty two wiper positions along the

resistive array.

The value of the counter is stored in nonvolatile memory

whenever each CS transitions HIGH while the pertaining

INC input is also HIGH. In order to avoid an accidental store

initial power-up. When left open, each CS pin is internally

The system may select the X93256, move any wiper and

deselect the device without having to store the latest wiper

position in nonvolatile memory. After the wiper movement is

performed as previously described and once the new

position is reached, the system must keep INC LOW while

taking CS HIGH. The new wiper position will be maintained

until changed by the system or until a power-up/down cycle

recalled the previously stored data. In order to recall the

stored position of the wiper on power-up, the CS pin must be

held HIGH.

This procedure allows the system to always power-up to a

preset value stored in nonvolatile memory; then during

system operation minor adjustments could be made. The

adjustments might be based on user preference, system

parameter changes due to temperature drift, or other system

trim requirements.

The state of U/D may be changed while CS remains LOW.

This allows the host system to enable the device and then

move each wiper up and down until the proper trim is

attained.

Symbol Table

Mode Selection

CS

INC

U/D

MODE

L

H

Wiper Up

L

L

Wiper Down

H

X

Store Wiper Position

H

X

X

Standby Current

L

X

No Store, Return to Standby

L

H

Wiper Up (not recommended)

L

L

Wiper Down (not recommended)

WAVEFORM

INPUTS

OUTPUTS

Must be

steady

Will be

steady

May change

from Low to

High

Will change

from Low to

High

May change

from High to

Low

Will change

from High to

Low

Don’t Care:

Changes

Allowed

Changing:

State Not

Known

N/A

Center Line

is High

Impedance

X93256