X9241A

Characteristics subject to change without notice.

7 of 18

REV 1.1.13 12/09/02

www.xicor.com

Figure 7. Acknowledge Response from Receiver

SCL from

Data Output

from Transmitter

1

89

START

Acknowledge

Master

Data Output

from Receiver

DETAILED OPERATION

All four XDCP potentiometers share the serial interface

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 X9241A contains four volatile Wiper Counter

Registers (WCR), one for each XDCP potentiometer.

The WCR can be 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 (DR0) upon

power-up.

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

lost when the X9241A is powered-down. Although the

register is automatically loaded with the value in DR0

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.