X9421 datasheet(4/21 Pages) XICOR

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X9421

REV 1.1.6 8/1/02

Characteristics subject to change without notice.

4 of 21

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PIN DESCRIPTIONS

Host Interface Pins

Serial Output (SO)

SO is a push/pull serial data output pin. During a read

cycle, data is shifted out on this pin. Data is clocked out

by the falling edge of the serial clock.

Serial Input

SI is the serial data input pin. All opcodes, byte

addresses and data to be written to the potentiometer

and pot register are input on this pin. Data is latched by

the rising edge of the serial clock.

Serial Clock (SCK)

The SCK input is used to clock data into and out of the

X9421.

Chip Select (CS)

When CS is HIGH, the X9421 is deselected and the

SO pin is at high impedance, and (unless an internal

write cycle is underway) the device will be in the

standby state. CS LOW enables the X9421, placing it

in the active power mode. It should be noted that after

a power-up, a HIGH to LOW transition on CS is

required prior to the start of any operation.

Hold (HOLD)

HOLD is used in conjunction with the CS pin to select

the device. Once the part is selected and a serial

sequence is underway, HOLD may be used to pause

the serial communication with the controller without

resetting the serial sequence. To pause, HOLD must

be brought LOW while SCK is LOW. To resume

communication, HOLD is brought HIGH, again while

SCK is LOW. If the pause feature is not used, HOLD

should be held HIGH at all times.

Device Address (A0)

The address input is used to set the least signiﬁcant bit

of the 8-bit slave address. A match in the slave address

serial data stream must be made with the address

input in order to initiate communication with the X9421.

A maximum of 2 devices may occupy the SPI serial

bus.

Potentiometer Pins

VH/RH, VL/RL

The VH/RH and VL/RL inputs are equivalent to the

terminal connections on either end of a mechanical

potentiometer.

VW/RW

The wiper output is equivalent to the wiper output of a

mechanical potentiometer.

Hardware Write Protect Input (WP)

The WP pin when LOW prevents nonvolatile writes to

the Data Registers. Writing to the Wiper Counter

System/Digital Supply (VCC)

VCC is the supply voltage for the system/digital section.

VSS is the system ground.

PRINCIPLES OF OPERATION

The

X9421

highly

integrated

microcircuit

incorporating a resistor array and associated registers

and counter and the serial interface logic providing

direct communication between the host and the XDCP

potentiometer.

Serial Interface

The X9421 supports the SPI interface hardware

conventions. The device is accessed via the SI input

with data clocked in on the rising SCK. CS must be

LOW and the HOLD and WP pins must be HIGH

during the entire operation.

The SO and SI pins can be connected together, since

they have three state outputs. This can help to reduce

system pin count.

Array Description

The X9421 is comprised of one resistor array

containing 63 discrete resistive segments that are

connected in series. The physical ends of each array

are equivalent to the ﬁxed terminals of a mechanical

potentiometer (VH/RH and VL/RL inputs).

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