X9279 Datasheet, PDF (5/24 Pages) Xicor Inc. – Single Digitally-Controlled (XDCP) Potentiometer

X9279
PRINCIPLES OF OPERATION
The X9279 is a integrated microcircuit incorporating a
resistor array and associated registers and counter
and the serial interface logic providing direct
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_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 each individual array only one
switch may be turned on at a time.
Figure 1. Detailed Potentiometer Block Diagram
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_CC and the voltages applied to the
potentiometer pins provided that V_CC is always more
positive than or equal to V_H, V_L, and V_W, i.e., V_CC ≥ V_H,
V_L, V_W. The V_CC ramp rate specification is always in
effect.
SERIAL DATA PATH
SERIAL
BUS
R_H
FROM INTERFACE
INPUT
CIRCUITRY
REGISTER 0
REGISTER 1
C
(DR0)
(DR1)
O
U
8
BANK_0 Only
8 PARALLEL
N
T
BUS
INPUT
E
R
REGISTER 2
(DR2)
REGISTER 3
(DR3)
WIPER
D
COUNTER ^E
REGISTER
(WCR)
C
O
D
E
INC/DEC
IF WCR = 00[H] THEN R_W = R_L
IF WCR = FF[H] THEN R_W = R_H
UP/DN
LOGIC
UP/DN
MODIFIED SCK _CLK
R_L
R_W
REV 1.1.7 2/6/03
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Characteristics subject to change without notice. 5 of 24