4
FN8175.4
September 23, 2009
Pinout
X9279
(14 LD TSSOP)
TOP VIEW
Pin Functions
Pin Descriptions
Bus Interface Pins
SERIAL DATA INPUT/OUTPUT (SDA)
The SDA is a bidirectional serial data input/output pin for a
2-Wire slave device and is used to transfer data into and out
of the device. It receives device address, opcode, wiper
register address and data sent from an 2-Wire master at the
rising edge of the serial clock SCL, and it shifts out data after
each falling edge of the serial clock SCL.
It is an open drain output and may be wire-ORed with any
number of open drain or open collector outputs. An open
drain output requires the use of a pull-up resistor. For
selecting typical values, refer to the guidelines for calculating
typical values on the bus pull-up resistors graph.
SERIAL CLOCK (SCL)
This input is used by 2-Wire master to supply 2-Wire serial
clock to the X9279.
DEVICE ADDRESS (A3 - A0)
The Address inputs A2 - A0 are used to set the least significant
3 bits of the 8-bit slave address, address pin A3 must be
connected to ground for proper operation. A match in the slave
address serial data stream must be made with the Address
input in order to initiate communication with the X9279. A
maximum of 8 devices may occupy the 2-Wire serial bus.
Potentiometer Pins
R
H
, R
L
The R
H
and R
L
pins are equivalent to the terminal
connections on a mechanical potentiometer.
R
W
The wiper pin is equivalent to the wiper terminal of a
mechanical potentiometer.
Bias 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 open. 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 X9279 is a integrated microcircuit incorporating a
resistor array and associated registers and counter and the
serial interface logic providing direct communication
between the host and the digitally controlled potentiometers.
This section provides detail description of the following:
• Resistor Array Description
• Serial Interface Description
• Instruction and Register Description
Array Description
The X9279 is comprised of a resistor array (see Figure 1).
The array contains, in effect, 255 discrete resistive segments
that are connected in series. The physical ends of each array
are equivalent to the fixed terminals of a mechanical
potentiometer (R
H
and R
L
inputs).
At both ends of each array and between each resistor
segment is a CMOS switch connected to the wiper (R
W
)
output. Within each individual array only one switch may be
turned on at a time.
These switches are controlled by a Wiper Counter Register
(WCR). The 8-bits of the WCR (WCR[7:0]) are decoded to
select, and enable, one of 256 switches (see Table 1).
The WCR may be written directly. These Data Registers can
the WCR can be read and written by the host system.
PIN
TSSOP SYMBOL FUNCTION
1 NC No Connect
2 A0 Device Address for 2-Wire bus
3 NC No Connect
4 A2 Device Address for 2-Wire bus
5 SCL Serial Clock for 2-Wire bus
6 SDA Serial Data Input/Output for 2-Wire bus
7V
SS
System Ground
8 WP Hardware Write Protect
9 A1 Device Address for 2-Wire bus
10 A3 Device Address for 2 wire-bus. Must be
connected to Ground
11 R
W
Wiper Terminal of the Potentiometer
12 R
H
High Terminal of the Potentiometer
13 R
L
Low Terminal of the Potentiometer
14 V
CC
System Supply Voltage
V
CC
R
L
V
SS
1
2
3
4
5
6
7
8
14
13
12
11
10
9
A0
R
W
SCL
A2
R
H
NC
NC
SDA
A3
WP
A1
X9279
