X9268 datasheet(6/22 Pages) RENESAS

6 / 22 page

X9268

FN8172 Rev.4.00

Page 6 of 22

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

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)

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