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Low Noise/Low Power/2-Wire Bus

X9409

Preliminary Information

Quad Digitally Controlled Potentiometers (XDCP

)

FEATURES

· Four potentiometers per package
· 64 resistor taps
· 2-wire serial interface for write, read, and trans-

fer operations of the potentiometer

· 50

Wiper resistance, typical at 5V.

· Four non-volatile data registers for each

potentiometer

· Non-volatile storage of multiple wiper position
· Power on recall. Loads saved wiper position on

power up.

· Standby current < 1µA typical
· System V

: 2.7V to 5.5V operation

· 10K

, 2.5K

End to end resistance

· 100 yr. data retention
· Endurance: 100,000 data changes per bit per

register

· Low power CMOS
· 24-lead SOIC, 24-lead TSSOP, and

24-lead CSP (Chip Scale Package) Packages

DESCRIPTION

The X9409 integrates 4 digitally controlled
potentiometers (XDCP) on a monolithic CMOS
integrated microcircuit.

The digitally controlled potentiometer is implemented
using 63 resistive elements in a series array. Between
each element are tap points connected to the wiper
terminal through switches. The position of the wiper on
the array is controlled by the user through the 2-wire
bus interface. Each potentiometer has associated with
it a volatile Wiper Counter Register (WCR) and 4
nonvolatile Data Registers (DR0:DR3) that can be
directly written to and read by the user. The contents
of the WCR controls the position of the wiper on the
resistor array through the switches. Power up recalls
the contents of DR0 to the WCR.

The XDCP can be used as a three-terminal
potentiometer or as a two-terminal variable resistor in
a wide variety of applications including control,
parameter adjustments, and signal processing.

BLOCK DIAGRAM

Interface

and

Control

Circuitry

SCL

SDA

A0
A1
A2
A3

Wiper

Counter

(WCR)

Resistor

Array
Pot 1

Wiper

Counter

(WCR)

Data

Resistor

Array

Resistor

Array

Wiper

Counter

(WCR)

Wiper

Counter

(WCR)

Pot 3

Pot 2

Pot 0

PPLICATION

OTES

A V A I L A B L E

AN99 · AN115 · AN120 · AN124 · AN133 · AN134 · AN135

X9409

 Preliminary Information

Characteristics subject to change without notice.

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PIN DESCRIPTIONS

Host Interface Pins

Serial Clock (SCL)

The SCL input is used to clock data into and out of the
X9409.

Serial Data (SDA)

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
values, refer to the guidelines for calculating typical
values on the bus pull-up resistors graph.

Device Address (A

)

The address inputs are used to set the least significant
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 X9409. A maximum of 16 devices may occupy the
2-wire serial bus.

Potentiometer Pins

, V

The V

and V

inputs are equivalent to the

terminal connections on either end of a mechanical
potentiometer.

The wiper outputs are 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.

PIN NAMES

Symbol

Description

SCL

Serial Clock

SDA

Serial Data

A0-A3

Device Address

Potentiometer Pin
(terminal equivalent)

Potentiometer Pin
(wiper equivalent)

Hardware Write Protection

System Supply Voltage

System Ground (Digital)

No Connection

PIN CONFIGURATION

SDA

SCL

SOIC

X9409

SDA

TSSOP

X9409

SCL

Top ViewBumps Down

A 0

SDA

SCL

CSP

X9409 Preliminary Information

Characteristics subject to change without notice.

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PRINCIPLES OF OPERATION

The X9409 is a highly integrated microcircuit
incorporating four resistor arrays and their associated
registers and counters and the serial interface logic
providing direct communication between the host and
the XDCP potentiometers.

Serial Interface

The X9409 supports a bidirectional bus oriented
protocol. 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 provide the clock for both transmit and receive
operations. Therefore, the X9409 will be considered a
slave device in all applications.

Clock and Data Conventions

Data states on the SDA line can change only during
SCL LOW periods (t

LOW

). SDA state changes during

SCL HIGH are reserved for indicating start and stop
conditions.

Start Condition

All commands to the X9409 are preceded by the start
condition, which is a HIGH to LOW transition of SDA
while SCL is HIGH (t

HIGH

). The X9409 continuously

monitors the SDA and SCL lines for the start condition
and will not respond to any command until this
condition is met.

Stop Condition

All communications must be terminated by a stop
condition, which is a LOW to HIGH transition of SDA
while SCL is HIGH.

Acknowledge

Acknowledge is a software convention used to provide
a positive handshake between the master and slave
devices on the bus to indicate the successful receipt of
data. The transmitting device, either the master or the
slave, will release the SDA bus after transmitting eight
bits. The master generates a ninth clock cycle and
during this period the receiver pulls the SDA line LOW
to acknowledge that it successfully received the eight
bits of data.

The X9409 will respond with an acknowledge after
recognition of a start condition and its slave address
and once again after successful receipt of the
command byte. If the command is followed by a data
byte the X9409 will respond with a final acknowledge.

Array Description

The X9409 is comprised of four resistor arrays. Each
array contains 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 (V

and V

inputs).

At both ends of each array and between each resistor
segment is a CMOS switch connected to the wiper
(V

) output. Within each individual array only one

switch may be turned on at a time. These switches are
controlled by the Wiper Counter Register (WCR). The
six bits of the WCR are decoded to select, and enable,
one of sixty-four switches.

The WCR may be written directly, or it can be changed
by transferring the contents of one of four associated
Data Registers into the WCR. These Data Registers
and the WCR can be read and written by the host
system.

Device Addressing

Following a start condition the master must output the
address of the slave it is accessing. The most
significant four bits of the slave address are the device
type identifier (refer to Figure 1 below). For the X9409
this is fixed as 0101[B].

Figure 1. Slave Address

The next four bits of the slave address are the device
address. The physical device address is defined by the
state of the A0-A3 inputs. The X9409 compares the
serial data stream with the address input state; a
successful compare of all four address bits is required
for the X9409 to respond with an acknowledge. The
A

inputs can be actively driven by CMOS input

signals or tied to V

or V

Device Type

Identifier

Device Address

X9409 Preliminary Information

Characteristics subject to change without notice.

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Acknowledge Polling

The disabling of the inputs, during the internal
nonvolatile write operation, can be used to take
advantage of the typical nonvolatile write cycle time.
Once the stop condition is issued to indicate the end of
the nonvolatile write command the X9409 initiates the
internal write cycle. ACK polling can be initiated
immediately. This involves issuing the start condition
followed by the device slave address. If the X9409 is
still busy with the write operation no ACK will be
returned. If the X9409 has completed the write
operation an ACK will be returned and the master can
then proceed with the next operation.

Flow 1. ACK Polling Sequence

Instruction Structure

The next byte sent to the X9409 contains the
instruction and register pointer information. The format
is shown in Figure 2.

Figure 2. Instruction Byte Format

The four high order bits define the instruction. The next
two bits (R1 and R0) select one of the four registers
that is to be acted upon when a register oriented
instruction is issued. The last bits (P1, P0) select
which one of the four potentiometers is to be affected
by the instruction.

Four of the nine instructions end with the transmission
of the instruction byte. The basic sequence is
illustrated in Figure 3. These two-byte instructions
exchange data between the Wiper Counter Register
and one of the data registers. A transfer from a Data
Register to a Wiper Counter Register is essentially a
write to a static RAM. The response of the wiper to this
action will be delayed t

WRL

. A transfer from the Wiper

Counter Register (current wiper position), to a Data
Register is a write to nonvolatile memory and takes a
minimum of t

to complete. The transfer can occur

between one of the four potentiometers and one of its
associated registers; or it may occur globally, wherein
the transfer occurs between all of the potentiometers
and one of their associated registers.

Four instructions require a three-byte sequence to
complete. These instructions transfer data between
the host and the X9409; either between the host and
one of the data registers or directly between the host
and the Wiper Counter Register. These instructions
are: Read Wiper Counter Register (read the current
wiper position of the selected pot), Write Wiper
Counter Register (change current wiper position of the
selected pot), Read Data Register (read the contents
of the selected nonvolatile register) and Write Data
Register (write a new value to the selected Data
Register). The sequence of operations is shown in
Figure 4.

Nonvolatile Write

Command Completed

Enter ACK Polling

Issue

START

Issue Slave

Address

ACK

Returned?

Further

Operation?

Issue

Instruction

Issue STOP

YES

Proceed

Issue STOP

Proceed

Pot Select

Select

Instructions

X9409 Preliminary Information

Characteristics subject to change without notice.

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Figure 3. Two-Byte Instruction Sequence

S
T
A
R
T

A
C
K

P1 P0

A
C
K

SCL

SDA

S
T
O
P

The Increment/Decrement command is different from
the other commands. Once the command is issued and
the X9409 has responded with an acknowledge, the
master can clock the selected wiper up and/or down in
one segment steps; thereby, providing a fine tuning
capability to the host. For each SCL clock pulse (t

HIGH

)

while SDA is HIGH, the selected wiper will move one

resistor segment towards the V

terminal. Similarly,

for each SCL clock pulse while SDA is LOW, the
selected wiper will move one resistor segment towards
the V

terminal. A detailed illustration of the

sequence and timing for this operation are shown in
Figures 5 and 6 respectively.

Table 1. Instruction Set

Note:

(7) 1/0 = data is one or zero

Instruction

Instruction Set

Operation

Read Wiper Counter
Register

Read the contents of the Wiper Counter
Register pointed to by P

Write Wiper Counter
Register

Write new value to the Wiper Counter Register
pointed to by P

Read Data Register

Read the contents of the Data Register pointed
to by P

and R

Write Data Register

Write new value to the Data Register pointed to
by P

and R

XFR Data Register to
Wiper Counter Register

Transfer the contents of the Data Register
pointed to by P

and R

to its associated

Wiper Counter Register

XFR Wiper Counter
Register to Data
Register

Transfer the contents of the Wiper Counter
Register pointed to by P

to the Data

Global XFR Data
Registers to Wiper
Counter Registers

Transfer the contents of the Data Registers
pointed to by R

of all four pots to their

respective Wiper Counter Registers

Global XFR Wiper
Counter Registers to
Data Register

Transfer the contents of both Wiper Counter
Registers to their respective Data Registers
pointed to by R

of all four pots

Increment/Decrement
Wiper Counter Register

Enable Increment/decrement of the WCR Latch
pointed to by P

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