X9241A

Characteristics subject to change without notice.

8 of 18

REV 1.1.13 12/09/02

www.xicor.com

Figure 8. Detailed Potentiometer Block Diagram

Serial Data Path

From Interface

Circuitry

Register 0

Register 1

Register 2

Register 3

Serial

Bus

Input

Parallel

Bus

Input

Wiper

Counter

Register

INC/DEC

Logic

UP/DN

CLK

Modified SCL

UP/DN

8

6

C

D

e

o

u

n

t

e

r

e

c

o

d

Cascade

DW

CM

Control

Logic

2

Cascade Mode

The X9241A provides a mechanism for cascading the

arrays. That is, the sixty-three resistor elements of one

array may be cascaded (linked) with the resistor

lower order array (See Figure 9).

Cascade Control Bits

The data byte, for the three-byte commands, contains 6

bits (LSBs) for defining the wiper position plus two high

order bits, CM (Cascade Mode) and DW (Disable

Wiper, normal operation).

The state of the CM bit (bit 7 of WCR) enables or

disables cascade mode. When the CM bit of the WCR

is set to “0” the potentiometer is in the normal operation

mode. When the CM bit of the WCR is set to “1” the

potentiometer is cascaded with its adjacent higher

order potentiometer. For example; if bit 7 of WCR2 is

set to “1”, pot 2 will be cascaded to pot 3.

The state of DW enables or disables the wiper. When

the DW bit of the WCR is set to “0” the wiper is enabled;

when set to “1” the wiper is disabled. If the wiper is

disabled, the wiper terminal will be electrically isolated

and float.

the wiper terminals of the cascaded arrays must be

electrically connected externally. All but one of the

wipers must be disabled. The user can alter the wiper

position by writing directly to the WCR or indirectly by

transferring the contents of the Data Registers to the

WCR or by using the Increment/Decrement command.

When using the Increment/Decrement command the

wiper position will automatically transition between

arrays. The current position of the wiper can be

determined by reading the WCR registers; if the DW bit

is “0”, the wiper in that array is active. If the current

wiper position is to be maintained on power-down a

global XFR WCR to Data Register command must be

issued to store the position in NV memory before

power-down.