X9313
3
DEVICE OPERATION
There are three sections of the X9313: 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 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
X9313 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 thirty two 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 X9313 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 X9313, move the wiper and
deselect the device without having to store the latest
wiper position in nonvolatile memory. The wiper move-
ment 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 X9313
and then move the wiper up and down until the proper
trim is attained.
T
IW
/R
TOTAL
The electronic switches on the X9313 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
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
