X9271 Xicor, X9271 Datasheet - Page 5

• Manufacturer Part Number: X9271
• Description: Single Digitally-Controlled (XDCP) Potentiometer
• Manufacturer: Xicor

X9271
PRINCIPLES OF OPERATION
Device Description
S
The X9271 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.
A
The X9271 is comprised of a resistor array (see Figure
1). The array contains the equivalent of 255 discrete
resistive segments that are connected in series. The
Figure 1. Detailed Potentiometer Block Diagram
REV 1.1.7 2/6/03
ERIAL
RRAY
IF WCR = 00[H] THEN R
IF WCR = FF[H] THEN R
D
I
NTERFACE
SERIAL DATA PATH
FROM INTERFACE
ESCRIPTION
CIRCUITRY
W
W
= R
= R
L
H
REGISTER 2
REGISTER 0
(DR0)
(DR2)
BANK_0 Only
8
REGISTER 1
REGISTER 3
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MODIFIED SCK
(DR1)
(DR3)
UP/DN
physical ends of each array are equivalent to the fixed
terminals of a mechanical potentiometer (R
inputs).
At both ends of each array and between each resistor
segment is a CMOS switch connected to the wiper
(R
switch may be turned on at a time.
These switches are controlled by a Wiper Counter
Register (WCR). The 8-bits of the WCR (WCR[7:0])
are decoded to select, and enable, one of 256 switches
(see Table 1).
P
There are no restrictions on the power-up or power-
down conditions of V
potentiometer pins provided that V
positive than or equal to V
V
effect.
8
OWER
L
W
, V
) output. Within each individual array only one
W
U
. The V
PARALLEL
BUS
INPUT
UP/DN
CLK
SERIAL
BUS
INPUT
P AND
REGISTER
COUNTER
INC/DEC
LOGIC
WIPER
(WCR)
D
CC
OWN
Characteristics subject to change without notice.
ramp rate specification is always in
R
CC
ECOMMENDATIONS
C
O
U
N
T
E
R
D
E
C
O
D
E
and the voltages applied to the
H
, V
L
, and V
CC
.
W
is always more
, i.e., V
R
R
R
H
H
L
W
CC
and R
5 of 23
≥ V
H
L
,