X9221
PIN DESCRIPTIONS
Host Interface Pins
Serial Clock (SCL)
PIN NAMES
Symbol
Description
Serial Clock
SCL
SDA
Serial Data
Address
The SCL input is used to clock data into and out of the
X9221.
A0–A3
V
V
/R –V /R
,
Potentiometers
(terminal equivalent)
H0 H0 H1 H1
/R –V /R
L0 H0 L1 L0
Serial Data (SDA)
V
/R –V /R
Potentiometers
(wiper equivalent)
W0 W0 W1 W1
SDA is a bidirectional pin used to transfer data into
and out of the device. 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 val-
ues, refer to the guidelines for calculating typical val-
ues on the bus pull-up resistors graph.
RES
Reserved (Do not connect)
PRINCIPLES OF OPERATION
The X9221 is a highly integrated microcircuit incorpo-
rating two resistor arrays, their associated registers
and counters and the serial interface logic providing
direct communication between the host and the XDCP
potentiometers.
Address
The Address inputs are used to set the least signifi-
cant 4 bits 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 X9221
Serial Interface
The X9221 supports a bidirectional bus oriented proto-
col. The protocol defines any device that sends data
onto the bus as a transmitter and the receiving device
as the receiver. The device controlling the transfer is a
master and the device being controlled is the slave.
The master will always initiate data transfers and pro-
vide the clock for both transmit and receive operations.
Therefore, the X9221 will be considered a slave device
in all applications.
Potentiometer Pins
V /R (V /R –V /R ), V /R (V /R –V /R )
H
H
H0 H0 H1 H1
L
L
L0 L0 L1 L1
The V /R and V /R inputs are equivalent to the ter-
H
H
L
L
minal connections on either end of a mechanical
potentiometer.
V /R (V /R –V /R )
ꢀ0 ꢀ0 ꢀ1 ꢀ1
Clock and Data Conventions
ꢀ
ꢀ
The wiper outputs are equivalent to the wiper output of
a mechanical potentiometer.
Data states on the SDA line can change only during
SCL LOW periods (t
). SDA state changes during
LOW
SCL HIGH are reserved for indicating start and stop
conditions.
PIN CONFIGURATION
Start Condition
DIP/SOIC
All commands to the X9221 are preceded by the start
condition, which is a HIGH to LOW transition of SDA
V
/R
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
V
CC
W0 W0
while SCL is HIGH (t
). The X9221 continuously
V
/R
RES
RES
RES
A1
L0 L0
HIGH
monitors the SDA and SCL lines for the start condition,
and will not respond to any command until this condi-
tion is met.
V
/R
H0 L0
A0
A2
X9221
V
/R
A3
W1 W1
Stop Condition
V
/R
SCL
RES
RES
RES
L1 L1
All communications must be terminated by a stop con-
dition, which is a LOW to HIGH transition of SDA while
SCL is HIGH.
V
/R
H1 H1
SDA
V
SS
Characteristics subject to change without notice. 2 of 15
REV 1.1 8/8/02
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XICOR [ XICOR INC. ]
