X9251_07 Datasheet, PDF (4/20 Pages) Intersil Corporation – Quad Digitally-Controlled (XDCP™) Potentiometer

X9251
Pin Descriptions
Bus Interface Pins
SERIAL OUTPUT (SO)
SO is a 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)
SI is the serial data input pin. All opcodes, byte addresses
and data to be written to the device registers 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
X9251.
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 (A1 AND A0)
The address inputs are used to set the two least significant
bits of the 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 X9251. Device pins A1 and
A0 must be tied to a logic level which specifies the internal
address of the device, see Figures 2, 3, 4, 5 and 6.
CHIP SELECT (CS)
When CS is HIGH, the X9251 is deselected and the SO pin
is at high impedance, and (unless an internal write cycle is
underway) the device is in the standby state. CS LOW
enables the X9251, 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.
Potentiometer Pins
R_H, R_L
The R_H and R_L pins are equivalent to the terminal
connections on a mechanical potentiometer. Since there are
4 potentiometers, there are 4 sets of R_H and R_L such that
R_H0 and R_L0 are the terminals of DCP0 and so on.
R_W
The wiper pin are equivalent to the wiper terminal of a
mechanical potentiometer. Since there are 4 potentiometers,
there are 4 sets of R_W such that R_W0 is the terminals of
DCP0 and so on.
Supply Pins
SYSTEM SUPPLY VOLTAGE (V_CC) AND SUPPLY
GROUND (V_SS)
The V_CC pin is the system supply voltage. The V_SS pin is
the system ground.
Other Pins
NO CONNECT
No connect pins should be left floating. This pins are
used for Intersil manufacturing and testing purposes.
HARDWARE WRITE PROTECT INPUT (WP)
The WP pin when LOW prevents non-volatile writes to the
Data Registers.
Principles of Operation
The X9251 is an integrated circuit incorporating four DCPs
and their associated registers and counters, and a 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 (R_H and R_L pins). The RW pin is an
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).
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FN8166.5
April 13, 2007