X9312
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.
T
IW
/R
TOTAL
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-
tiple taps are connected to the wiper for t
IW
(INC to V
W
change). The R
TOTAL
value for the device can tempo-
rarily be reduced by a significant amount if the wiper is
moved several positions.
R
TOTAL
with V
CC
Removed
The end to end resistance of the array will fluctuate once
V
CC
is removed.
SYMBOL TABLE
WAVEFORM
INPUTS
Must be
steady
May change
from LOW
to HIGH
May change
from HIGH
to LOW
Don’t Care:
Changes
Allowed
N/A
OUTPUTS
Will be
steady
Will change
from LOW
to HIGH
Will change
from HIGH
to LOW
Changing:
State Not
Known
Center Line
is High
Impedance
3
XICOR [ XICOR INC. ]
