X9279

Characteristics subject to change without notice.

10 of 24

REV 1.1.7 2/6/03

www.xicor.com

Table 4. Wiper counter Register, WCR (8-bit), WCR[7:0]: Used to store the current wiper position (Volatile, V).

Table 5. Data Register, DR (8-bit), Bit [7:0]: Used to store wiper positions or data (Nonvolatile, NV).

WCR7

WCR6

WCR5

WCR4

WCR3

WCR2

WCR1

WCR0

VVVVVVVV

(MSB)

(LSB)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

NV

NV

NV

NV

NV

NV

NV

NV

MSB

LSB

Instructions

Four of the seven instructions are three bytes in length.

These instructions are:

– Read Wiper Counter Register – read the current

wiper position of the potentiometer,

– Write Wiper Counter Register – change current

wiper position of the potentiometer,

– Read Data Register – read the contents of the

selected Data Register;

– Write Data Register – write a new value to the

selected Data Register.

The basic sequence of the three byte instructions is

illustrated in Figure 4. These three-byte instructions

exchange data between the WCR and one of the Data

Registers. A transfer from a Data Register to a WCR is

essentially a write to a static RAM, with the static RAM

controlling the wiper position. The response of the

from the WCR (current wiper position), to a Data

Register is a write to nonvolatile memory and takes a

between the potentiometer and one of its four

associated registers (Bank 0).

Two instructions require a two-byte sequence to

complete. These instructions transfer data between the

host and the X9279; either between the host and one

of the data registers or directly between the host and

the Wiper Counter Register. These instructions are:

– XFR Data Register to Wiper Counter Register –

This transfers the contents of one specified Data

Register to the Wiper Counter Register.

– XFR Wiper Counter Register to Data Register –

This transfers the contents of the Wiper Counter

Register to the specified Data Register.

The final command is Increment/Decrement (Figure 5

and

6). The

Increment/Decrement

command

is

different

from

the

other

commands.

Once

the

command is issued and the X9279 has responded with

an acknowledge, the master can clock the selected

wiper up and/or down in one segment steps; thereby,

providing a fine tuning capability to the host. For each

selected wiper will move one resistor segment towards

while SDA is LOW, the selected wiper will move one

See Instruction format for more details.

Figure 3. Two-Byte Instruction Sequence

These commands only valid when P1=P0=0

S

T

A

R

T

0

101

0 A2

A0

A

C

K

I3

I2 I1 I0

RB RA P1

A

C

K

SCL

SDA

S

T

O

P

00

ID3 ID2 ID1 ID0

P0

Device ID

Internal

Instruction

Opcode

Address

Register

Address

Pot/Bank

Address

A1