ISL97649A

16

FN7928.0

December 5, 2011

Read Operation

A read operation consists of a three-byte instruction followed by

one or more Data Bytes (see Figure 18). The master initiates the

operation issuing the following sequence: a START, the

Identification byte with the R/W bit set to "0", an Address Byte, a

second START, and a second Identification byte with the R/W bit

set to "1". After each of the three bytes, the ISL97649A responds

with an ACK; then the ISL97649A transmits the Data Byte. The

master then terminates the read operation (issuing a STOP

condition) following the last bit of the Data Byte (see Figure 16).

The byte at address 02h determines if the Data Bytes being read

are from volatile or non-volatile memory.

Communication with ISL97649A

There are three register addresses in the ISL97649A, 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.

Register Description: 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 0 or 1. Power-up

default for this address is 00h.

Register Description: IVP and WR

The output of the DCP is controlled directly by the WR. Writes and

reads can be made directly to this register to control and monitor

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 DCP output.

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 and 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.

Therefore, 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.

Writing a new value to the IVR

Write to ACR first

01010000

A00000010

A00000000

A

Then, write to IVR

01010000

A00000000

A

D0

D7

D6

D5

D4

D3

D2

D1

A

Note that the WR will also reflect this new value since both registers get writen at the same time

D0:LSB, D7:MSB

Writing a new value to WR only

Write to ACR first

01010000

A00000010

A10000000

A

Then, write to WR

01010000

A00000000

A

D0

D7

D6

D5

D4

D3

D2

D1

A

Note that the IVR value will NOT change

D0:LSB, D7:MSB

Reading from IVR

Write to the ACR first

01010000

A00000010

A00000000

A

Then set the IVR address

01010000

A00000000

A

Read from the IVR

01010001

A

D0

D7

D6

D5

D4

D3

D2

D1

Example 2

Reading from the WR

Write to the ACR first

01010000

A00000010

A10000000

A

Then set the WR address

01010000

A00000000

A

Read from the WR

01010001

A

D0

D7

D6

D5

D4

D3

D2

D1