X9312

3

DEVICE OPERATION

There are three sections of the X9312: the input control,

counter and decode section; the nonvolatile memory;

and the resistor array. The input control section oper-

ates 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 re-

tained 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 electronic

switch that transfers the potential at that point to the

wiper.

The

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

wiper along the resistor array. With

CS set LOW the

X9312 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 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 value of the counter is stored in nonvolatile memory

whenever

CS transistions HIGH while the INC input is

also HIGH.

When the X9312 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.

Operation Notes

The system may select the X9312, move the wiper and

deselect the device without having to store the latest

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 position

would be maintained until changed by the system or

until a power-up/down 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 X9312

and then move the wiper up and down until the proper

trim is attained.

The electronic switches on the X9312 operate in a

“make before break” mode when the wiper changes tap

positions. If the wiper is moved several positions mul-

rarily be reduced by a significant amount if the wiper is

moved several positions.

The end to end resistance of the array will fluctuate once

SYMBOL TABLE

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