X9259

5

FN8169.6

December 12, 2014

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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 potentiometer

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

specification is always in effect.

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 “Instructions” section on page 8 for more

details). Finally, it is loaded with the contents of its data register

zero (DR#0) upon power-up, (see Figure 1 on page 4).

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 AN162).

Data Registers (DR)

Each of the four DCPs has four 8-bit nonvolatile 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 nonvolatile 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).

WCR7

WCR6

WCR5

WCR4

WCR3

WCR2

WCR1

WCR0

(MSB)

(LSB)

TABLE 2. DATA REGISTER, DR (8-BIT), BIT [7:0]: USED TO STORE WIPER POSITIONS OR DATA (NONVOLATILE).

BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0

(MSB)

(LSB)