X9C102/103/104/503
3
DEVICE OPERATION
There are three sections of the X9C102/103/104/503:
the input control, counter and decode section; the non-
volatile 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 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
X9C102/103/104/503 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 X9C102/103/104/503 is powered-down, the
last counter position stored will be maintained in the
nonvolatile memory. When power is restored, the con-
tents of the memory are recalled and the counter is reset
to the value last stored.
OPERATION NOTES
The system may select the X9C102/103/104/503, 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-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
X9C102/103/104/503 and then move the wiper up and
down until the proper trim is attained.
T
IW
/R
TOTAL
The electronic switches on the X9C102/103/104/503
operate in a “make before break” mode when the wiper
changes tap positions. If the wiper is moved several
positions, multiple taps are connected to the wiper for
t
IW
(INC to V
W
change). The R
TOTAL
value for the device
can temporarily 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
