3

FN8160.1

September 12, 2005

the resistor array. The 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. The resistor

array is comprised of 15 individual resistors connected in

series. At either end of the array and between each resistor

is an electronic switch that transfers the potential at that

point to the wiper pin.

The 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.

The electronic switches on the device operate in a “make

before break” mode when the wiper changes tap positions. If

the wiper is moved several positions, multiple taps are

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. When

power is restored, the contents of the memory are recalled

and the wiper is set to the value last stored.

Instructions and Programming

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

wiper along the resistor array. With CS set LOW, the device

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 four

bit counter. The output of this counter is decoded to select

one of 16 wiper positions along the resistive array.

The value of the counter is stored in nonvolatile memory

whenever CS transitions HIGH while the INC input is also

HIGH.

The system may select the X9116, move the wiper, and

deselect the device without having to store the latest wiper

position in nonvolatile memory. After the wiper movement is

performed as described above 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

recalls the previously stored data.

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, etc.

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

This allows the host system to enable the device and then

move the 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

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

X9116