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FN8177.7
October 7, 2015
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Chip Select (CS)
The device is selected when the CS input is LOW. The current
counter value is stored in nonvolatile memory when CS
is
returned HIGH while the INC
input is also HIGH. After the
store operation is complete, the X9313 will be placed in the
low power standby mode until the device is selected once
again.
Principles of 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 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, 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.
When the device is powered-down, the last wiper position
stored will be maintained in the nonvolatile memory. When
power is restored, the contents of the memory are recalled
and the wiper is set 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 thirty-two wiper positions along the resistive array.
The value of the counter is stored in nonvolatile memory
whenever CS
transitions HIGH while the INC input is also
HIGH.
The system may select the X9313, move the wiper and
deselect the device without having to store the latest wiper
position in nonvolatile memory. After the wiper movement is
performed as previously described and once the new
position is reached, the system must keep INC
LOW while
taking CS
HIGH. The new wiper position will be maintained
until changed by the system or until a power-up/down cycle
recalled the previously stored data.
This procedure allows 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.
Pinouts
X9313
(8 LD PDIP, 8 LD SOIC)
TOP VIEW
X9313
(8 LD MSOP)
TOP VIEW
TABLE 1. PIN NAMES
SYMBOL DESCRIPTION
RH/VH High terminal
RW/VW Wiper terminal
RL/VL Low terminal
VSS Ground
VCC Supply voltage
U/D
Up/Down control input
INC Increment control input
CS Chip Select control input
VCC
CS
INC
U/D
RH/VH
VSS
1
2
3
4
8
7
6
5
X9313
RL/VL
RW/VW
VCC
CS
U/D
RH/VH
1
2
3
4
8
7
6
5
X9313
RL/VL
RW/VW
INC
VSS
TABLE 2. MODE SELECTION
CS
INC U/D MODE
L H Wiper up
L L Wiper down
H X Store wiper position
H X X Standby current
X9313
