4

FN8179.2

December 21, 2009

Pin Configuration

X9315

(8 LD MSOP, SOIC, PDIP)

TOP VIEW

Pin Description

are equivalent to the fixed terminals of a mechanical

references the relative position of the terminal in relation to

wiper movement direction selected by the U/D input, and not

the voltage potential on the terminal.

R

W

/V

W

terminal of a mechanical potentiometer. The position of the

wiper within the array is determined by the control inputs.

The wiper terminal series resistance is typically 200

Ω at

Up/Down (U/D)

The U/D input controls the direction of the 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

counter in the direction indicated by the logic level on the

U/D input.

Chip Select (CS)

The device is selected when the CS input is LOW. The

current counter value is stored in nonvolatile memory when

CS is returned HIGH while the INC input is also HIGH. After

the store operation is complete the X9315 will be placed in

the low power standby mode until the device is selected

once again.

Principles of Operation

There are three sections of the X9315: the input control,

counter and decode section; the nonvolatile memory; and

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 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.

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 five

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 CS transitions HIGH while the INC input is also

HIGH.

The system may select the X9315, 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

Pin Names

SYMBOL

DESCRIPTION

RH/VH

High terminal

RW/VW

Wiper terminal

RL/VL

Low terminal

VSS

Ground

VCC

Supply voltage

U/D

Up/Down control input

INC

Increment control input

CS

Chip Select control input

CS

INC

U/D

1

2

3

4

8

7

6

5

X9315

X9315