X9C303

Characteristics subject to change without notice.

3 of 10

REV 1.1 4/27/01

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PRINCIPLES OF OPERATION

There are three sections of the X9C303: the input con-

trol, counter and decode section; the nonvolatile mem-

ory; 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 99 individual resistors connected in series. At either

end of the array and between each resistor is an elec-

tronic switch that transfers the potential 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,

porarily be reduced by a significant amount if the wiper

is moved several positions.

When the device is powered-down, the last counter

position stored will be maintained in the nonvolatile

memory. When power is restored, the contents of the

memory are recalled and the counter is reset 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 seven-bit counter. The output of this

counter is decoded to select one of one-hundred wiper

positions along the resistive array.

The value of the counter is stored in nonvolatile mem-

ory whenever CS transitions HIGH while the INC input

is also HIGH.

The system may select the X9C303, move the wiper,

and deselect the device without having to store the lat-

est wiper position in nonvolatile memory. The wiper

movement is performed as described above; once the

new position is reached, the system would the keep

INC LOW while taking CS HIGH. The new wiper posi-

tion would be maintained until changed by the system

or until a power-down/up cycle recalled the previously

stored data.

This would allow 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.

MODE SELECTION

SYMBOL TABLE

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