X9421 datasheet(5/21 Pages) XICOR

5 / 21 page

X9421

REV 1.1.6 8/1/02

Characteristics subject to change without notice.

5 of 21

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At both ends of the array and between each resistor

segment is a CMOS switch connected to the wiper

(VW/RW) output. Within the individual array only one

switch may be turned on at a time.

These switches are controlled by a Wiper Counter

to select, and enable, one of sixty-four switches. The

block diagram of the potentiometer is shown in Figure 1.

Wiper Counter Register (WCR)

The X9421 contains a Wiper Counter Register. The

WCR can be envisioned as a 6-bit parallel and serial

load counter with its outputs decoded to select one of

sixty-four

switches

along

its

resistor

array. The

contents of the WCR can be altered in four ways: it

may be written directly by the host via the Write Wiper

Counter Register instruction (serial load); it may be

written indirectly by transferring the contents of one of

four associated Data Registers via the XFR Data

one step at a time by the Increment/ Decrement

instruction. Finally, it is loaded with the contents of its

data register zero (DR0) upon power-up.

The Wiper Counter Register is a volatile register; that

is, its contents are lost when the X9421 is powered-

down. Although the register is automatically loaded

with the value in DR0 upon power-up, this may be

different from the value present at power-down.

Data Registers

The potentiometer has four 6-bit nonvolatile Data

Registers. These can be read or written directly by the

host. Data can also be transferred between any of the

four Data Registers and the WCR. It should be noted all

operations changing data in one of the Data Registers is

a nonvolatile operation and will take a maximum of 10ms.

If the application does not require storage of multiple

settings for the potentiometer, the Data Registers can

be used as regular memory locations for system

parameters or user preference data.

Table 1. Data Registers, (6-bit), Nonvolatile

There are four 6-bit Data Registers associated with the

potentiometer.

– {D5~D0}: These bits are for general purpose Nonvol-

atile data storage or for storage of up to four different

wiper values.

Table 2. Wiper Counter Register, (6-bit), Volatile

– {WP5~WP0}: These bits specify the wiper position of

the potentiometer.

(MSB)

(LSB)

WP5 WP4 WP3 WP2 WP1 WP0

(MSB)

(LSB)

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