10

FN8241.2

August 15, 2005

Communicating with the ISL95711

There are 3 register addresses in the ISL95711, of which two

can be used. Address 00h and address 02h are used to

control the device. Address 01h is reserved and should not

be used. Address 00h contains the non-volatile Initial Value

Register (IVR), and the volatile Wiper Register (WR).

Address 02h contains only a volatile word and is used as a

pointer to either the IVR or WR. See Table 1.

Register Descriptions: Access Control

The Access Control Register (ACR) is volatile and is at

address 02h. It is 8-bits, and only the MSB is significant, all

other bits should be zero (0). The ACR controls which word

is accessed at register 00h as follows:

00h = Nonvolatile IVR

80h = Volatile WR

All other bits of the ACR should be written to as zeros. Only

the MSB can be either 0 or 1. Power-up default for this

address is 00h.

Register Description: IVR and WR

The ISL95711 has a single potentiometer. The wiper of the

potentiometer is controlled directly by the WR. Writes and

reads can be made directly to this register to control and

monitor the wiper position without any non-volatile memory

changes. This is done by setting address 02h to data 80h,

then writing the data.

The non-volatile IVR stores the power-up value of the wiper.

On power-up, the contents of the IVR are transferred to the

WR.

To write to the IVR, first address 02h is set to data 00h, then

the data is written. Writing a new value to the IVR register

will set a new power-up position for the wiper. Also, writing to

this register will load the same value into the WR as the IVR.

So, if a new value is loaded into the IVR, not only will the

non-volatile IVR change, but the WR will also contain the

same value after the write, and the wiper position will

change. Reading from the IVR will not change the WR, if its

contents are different.

FIGURE 3. BYTE WRITE SEQUENCE

FIGURE 4. READ SEQUENCE

S

T

A

R

T

S

T

O

P

IDENTIFICATION

BYTE

ADDRESS

BYTE

DATA

BYTE

A

C

K

SIGNALS FROM

THE MASTER

SIGNALS FROM

THE ISL95711

A

C

K

0

0

0

11

A

C

K

WRITE

SIGNAL AT SDA

00 0 0

00 000

0

SIGNALS

FROM THE

MASTER

SIGNALS FROM

THE SLAVE

SIGNAL AT SDA

S

T

A

R

T

IDENTIFICATION

BYTE WITH

R/W=0

ADDRESS

BYTE

A

C

K

A

C

K

00

0

11

S

T

O

P

A

C

K

0

1

0

11

IDENTIFICATION

BYTE WITH

R/W=1

A

C

K

S

T

A

R

T

LAST READ

DATA BYTE

FIRST READ

DATA BYTE

A

C

K

00

00 0

0 0

0

0

ISL95711