X9221

7

DETAILED OPERATION

and share a common architecture. Each potentiometer

is comprised of a resistor array, a wiper counter register

and four data registers. A detailed discussion of the

register organization and array operation follows.

Wiper Counter Register

The X9221 contains two wiper counter registers (WCR),

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 WCR instruction (serial load); it may be

written indirectly by transferring the contents of one of

four associated data registers via the XFR Data Register

instruction (parallel load); it can be modified one step at

a time by the Increment/ Decrement instruction; finally,

it is loaded with the contents of its data register zero (R0)

upon power-up.

The WCR is a volatile register; that is, its contents are

lost when the X9221 is powered-down. Although the

register is automatically loaded with the value in R0

upon power-up, it should be noted this may be different

from the value present at power-down.

Data Registers

Each potentiometer has four nonvolatile data registers.

These can be read or written directly by the host and

data can be transferred between any of the four data

registers and the WCR. It should be noted all operations

changing data in one of these 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, these registers can be

used as regular memory locations that could possibly

store system parameters or user preference data.

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

VH

VL

VW

IF WCR = 00[H] THEN VW = VL

IF WCR = 3F[H] THEN VW = VH

8

6

C

O

U

N

T

E

R

D

E

C

O

D

E

3079 ILL F15