5

FN8169.2

September 16, 2005

Principles of Operation

The X9259 is an integrated circuit incorporating four DCPs

and their associated registers and counters, and the serial

interface providing direct communication between a host

and the potentiometers.

DCP Description

Each DCP is implemented with a combination of resistor

elements and CMOS switches. The physical ends of each

DCP are equivalent to the fixed terminals of a mechanical

intermediate node, equivalent to the wiper terminal of a

mechanical potentiometer.

The position of the wiper terminal within the DCP is

controlled by an 8-bit volatile Wiper Counter Register

(WCR).

Power Up and Down Recommendations

There are no restrictions on the power-up or power-down

Wiper Counter Register (WCR)

The X9259 contains four Wiper Counter Registers, one for

each potentiometer. The Wiper Counter Register can be

envisioned as a 8-bit parallel and serial load counter with its

outputs decoded to select one of 256 wiper positions 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

Wiper Counter Register 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 (see Instruction

section for more details). Finally, it is loaded with the

contents of its data register zero (DR#0) upon power-up.

(See Figure 1.)

The Wiper Counter Register is a volatile register; that is, its

contents are lost when the X9259 is powered-down.

Although the register is automatically loaded with the value

in DR#0 upon power-up, this may be different from the value

present at power-down. Power-up guidelines are

recommended to ensure proper loadings of the DR#0 value

into the WCR# (See Design Considerations Section).

Data Registers (DR)

Each of the four DCPs has four 8-bit non-volatile Data

Registers. These can be read or written directly by the host.

Data can also be transferred between any of the four data

registers and the associated Wiper Counter Register. All

operations changing data in one of the data registers is a

non-volatile operation and takes a maximum of 10ms.

If the application does not require storage of multiple

settings for the potentiometer, the Data Registers can be

used as regular memory locations for system parameters or

user preference data.

Bit [7:0] are used to store one of the 256 wiper positions

(0~255).

TABLE 1. WIPER COUNTER REGISTER, WCR (8-bit), WCR[7:0]: Used to store the current wiper position (Volatile).

TABLE 2. DATA REGISTER, DR (8-BIT), BIT [7:0]: Used to store wiper positions or data (Non-volatile).

WCR7

WCR6

WCR5

WCR4

WCR3

WCR2

WCR1

WCR0

(MSB)

(LSB)

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

(MSB)

(LSB)

X9259