X9268 datasheet(6/22 Pages) INTERSIL

6 / 22 page

FN8172.4

August 29, 2006

PRINCIPLES OF OPERATION

The X9268 is a integrated microcircuit incorporating

four resistor arrays and their associated registers and

counters 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 X9268 is comprised of a resistor array (See

Figure 1). Each array contains 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 (RH and RL

inputs).

At both ends of each array and between each resistor

segment is a CMOS switch connected to the wiper

(RW) output. Within each individual array only one

switch may be turned on at a time.

These switches are controlled by a Wiper Counter

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 Requirements.

At all times, the voltages on the potentiometer pins

must be less than V+ and more than V-. During power-

up and power-down, VCC, V+, and V- must reach their

final values within 1msecs of each other. The VCC

ramp rate spec is always in effect.

Figure 1. Detailed Potentiometer Block Diagram

SERIAL DATA PATH

FROM INTERFACE

CIRCUITRY

SERIAL

BUS

INPUT

PARALLEL

BUS

INPUT

COUNTER

INC/DEC

LOGIC

UP/DN

CLK

MODIFIED SCL

UP/DN

IF WCR = 00[H] THEN RW = RL

IF WCR = FF[H] THEN RW = RH

WIPER

(WCR)

One of Two Potentiometers

(DR0)

(DR1)

(DR2)

(DR3)

X9268

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