4

FN8162.4

July 9, 2008

The wiper pin are equivalent to the wiper terminal of a

mechanical potentiometer.

Bias Supply Pins

the system ground.

Other Pins

NO CONNECT

No connect pins should be left open. These pins are used for

Intersil manufacturing and testing purposes.

Principals of Operation

The X9119 is an integrated microcircuit incorporating a

resistor array and its associated registers and counters and

the serial interface logic providing direct communication

between the host and the digitally controlled potentiometer.

This section provides detail description of the following:

• Resistor Array Description

• Serial Interface Description

• Instruction and Register Description

Resistor Array Description

The X9119 is comprised of a resistor array. The array

contains, in effect, 1023 discrete resistive segments that are

connected in series (Figure 1). The physical ends of each

array are equivalent to the fixed terminals of a mechanical

At both ends of each array and between each resistor

output. Within each individual array only one switch may be

turned on at a time. These switches are controlled by the

Wiper Counter Register (WCR). The 10-bits of the WCR

(WCR[9:0]) are decoded to select, and enable, one of 1024

switches.

The WCR may be written directly. The Data Registers and

the WCR can be read and written by the host system.

Serial Interface Description

SERIAL INTERFACE

The X9119 supports a bidirectional bus oriented protocol.

The protocol defines any device that sends data onto the

bus as a transmitter and the receiving device as the receiver.

The device controlling the transfer is a master and the

device being controlled is the slave. The master will always

initiate data transfers and provide the clock for both transmit

and receive operations. Therefore, the X9119 will be

considered a slave device in all applications.

CLOCK AND DATA CONVENTIONS

Data states on the SDA line can change only during SCL

LOW periods. SDA state changes during SCL HIGH are

reserved for indicating start and stop conditions (Figure 3).

START CONDITION

All commands to the X9119 are preceded by the start

condition, which is a HIGH to LOW transition of SDA while

SCL is HIGH. The X9119 continuously monitors the SDA

and SCL lines for the start condition and will not respond to

any command until this condition is met (Figure 3).

SERIAL DATA PATH

FROM INTERFACE

REGISTER 0

SERIAL

BUS

INPUT

PARALLEL

BUS

INPUT

COUNTER

REGISTER

R H

R L

R

W

10

10

C

O

U

N

T

E

R

D

E

C

O

D

E

WIPER

(WCR)

(DR0)

CIRCUITRY

REGISTER 1

(DR1)

REGISTER 2

(DR2)

REGISTER 3

(DR3)

FIGURE 1. DETAILED POTENTIOMETER BLOCK DIAGRAM SERIAL INTERFACE DESCRIPTION

R

X9119