X9110_08 Datasheet, PDF (4/18 Pages) Intersil Corporation – Dual Supply/Low Power/1024-Tap/SPI Bus

X9110
SERIAL DATA PATH
SERIAL
RH
FROM INTERFACE
CIRCUITRY
BUS
INPUT
REGISTER 0
REGISTER 1
C
(DR0)
(DR1)
O
U
10
10
PARALLEL
BUS
N
T
INPUT
E
R
REGISTER 2
(DR2)
REGISTER 3
(DR3)
WIPER
D
COUNTER
E
REGISTER
C
(WCR)
O
D
E
If WCR = 000[HEX] then R_W = R_L
If WCR = 3FF[HEX] then R_W = R_H
RL
RW
FIGURE 1. DETAILED POTENTIOMETER BLOCK DIAGRAM
Potentiometer Pins
R_H, R_L
The R_H and R_L pins are equivalent to the terminal
connections on a mechanical potentiometer.
R_W
The wiper pin are equivalent to the wiper terminal of a
mechanical potentiometer.
Bias Supply Pins
SYSTEM SUPPLY VOLTAGE (V_CC) AND SUPPLY
GROUND (V_SS)
The V_CC pin is the system supply voltage. The V_SS pin is
the system ground.
ANALOG SUPPLY VOLTAGES (V+ AND V-)
These supplies are the analog voltage supplies for the
potentiometer. The V+ supply is tied to the wiper switches
while the V- supply is used to bias the switches and the
internal P+ substrate of the integrated circuit. Both of these
supplies set the voltage limits of the potentiometer.
Principles Of Operation
Device Description
SERIAL INTERFACE
The X9110 supports the SPI interface hardware conventions.
The device is accessed via the SI input with data clocked-in
on the rising SCK. CS must be LOW and the HOLD and WP
pins must be HIGH during the entire operation.
The SO and SI pins can be connected together, since they
have three state outputs. This can help to reduce system pin
count.
ARRAY DESCRIPTION
The X9110 is comprised of a resistor array (Figure 1). The
array contains the equivalent of 1023 discrete resistive
segments that are connected in series. The physical ends of
each array are equivalent to the fixed terminals of a
mechanical potentiometer (R_H and R_L inputs).
At both ends of each array and between each resistor
segment is a CMOS switch connected to the wiper (R_W)
output. Within the individual array only one switch may be
turned on at a time.
These switches are controlled by a Wiper Counter Register
(WCR). The 10-bits of the WCR (WCR[9:0]) are decoded to
select, and enable, one of 1024 switches.
WIPER COUNTER REGISTER (WCR)
The X9110 contains a Wiper Counter Register (see Table 1)
for the XDCP potentiometer. The WCR is equivalent to a
serial-in, parallel-out register/counter with its outputs
decoded to select one of 1024 switches along its resistor
array. The contents of the WCR can be altered in one of
three ways: (1) it may be written directly by the host via the
write Wiper Counter Register instruction (serial load); (2) it
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FN8158.3
February 13, 2008