X9279 Xicor, X9279 Datasheet - Page 5

• Manufacturer Part Number: X9279
• Description: Single Digitally-Controlled (XDCP) Potentiometer
• Manufacturer: Xicor

X9279
PRINCIPLES OF OPERATION
The X9279 is a integrated microcircuit incorporating a
resistor array and associated registers and counter
and
communication between the host and the digitally
controlled potentiometers. This section provides detail
description of the following:
– Resistor Array Description.
– Serial Interface Description.
– Instruction and Register Description.
Array Description
The X9279 is comprised of a resistor array (see Figure
1). The array contains, in effect, 255 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
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.
Figure 1. Detailed Potentiometer Block Diagram
REV 1.1.7 2/6/03
W
) output. Within each individual array only one
IF WCR = 00[H] THEN R
IF WCR = FF[H] THEN R
the
FROM INTERFACE
SERIAL DATA PATH
CIRCUITRY
serial
interface
W
W
= R
= R
L
REGISTER 2
REGISTER 0
H
logic
(DR0)
(DR2)
H
and R
providing
L
BANK_0 Only
inputs).
8
REGISTER 3
REGISTER 1
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direct
MODIFIED SCK
(DR3)
(DR1)
UP/DN
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).
The WCR may be written directly. These Data
Registers can the WCR can be read and written by the
host system.
Power Up and Down Recommendations.
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.
L
8
, V
W
. The V
SERIAL
BUS
INPUT
PARALLEL
BUS
INPUT
UP/DN
CLK
REGISTER
COUNTER
INC/DEC
LOGIC
WIPER
(WCR)
CC
Characteristics subject to change without notice.
ramp rate specification is always in
CC
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
CC
L
H
W
5 of 24
≥ V
H
,