X9259 datasheet(5/25 Pages) XICOR

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X9259

Characteristics subject to change without notice.

5 of 25

REV 1.2.3 4/30/02

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PRINCIPLES OF OPERATION

The X9259 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 X9259 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 Recommendations.

There are no restrictions on the power-up or power-

down conditions of VCC and the voltages applied to the

potentiometer pins provided that VCC is always more

positive than or equal to VH, VL, and VW, i.e., VCC ≥ VH,

VL, VW. The VCC ramp rate speciﬁcation 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 Four Potentiometers

(DR0)

(DR1)

(DR2)

(DR3)

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