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FEATURES

Six digitally controlled 64-position
potentiometers

3-wire serial port provides for reading and
setting each potentiometer

Devices can be cascaded for single processor
multi-device control

Standard resistance values:
-

DS1806-010

10 k

DS1806-050

50 k

DS1806-100

100 k

Operating Temperature Range:
- Industrial temperature: -40

C to +85

PIN DESCIPTION

- 3V or 5V Supply

RST

- Serial Port Reset Input

- Serial Port Data Input

CLK

- Serial Port Clock Input

OUT

- Cascade Data Output

H1 - H6

- High End terminal of Pot

W1 - W6

- Wiper Terminal of Pot

GND

- Ground

L1-3

- Low Terminal Pots 1 through 3

L4-6

- Low Terminal Pots 4 through 6

PIN ASSIGNMENT

DESCRIPTION

The DS1806 Digital Sextet Potentiometer is a six-channel, digitally controlled, solid-state linear
potentiometer. Each potentiometer is comprised of 63 equiresistive sections as illustrated in the block
diagram of Figure 1. Each potentiometer has three terminals accessible to the user. These include the high
side terminals, H

, the wiper terminals, W

, and the low-end terminals, L1-3 and L4-6. Potentiometers 1

through 3 share the same low-end terminal L1-3; likewise, potentiometers 4 through 6 share the low-end
terminal L4-6.

Each wiper's position is selected via an 8-bit register value. Communication and control of the device is
accomplished via a 3-wire serial port interface. This interface in conjunction with a cascade output allows
the value of the device wiper settings to be read.

DS1806

Digital Sextet Potentiometer

www.dalsemi.com

L1-3

L4-6

RST

CLK

GND

OUT

DS1806 20-Pin DIP (300-mil)
DS1806S 20-Pin SOIC (300-mil)
DS1806E 20-Pin TSSOP (173-mil)
See Mech. Drawings Section

DS1806

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For multiple device and single processor environments, the DS1806 can be cascaded or daisy-chained.
This feature allows a single processor to control multiple devices.

The DS1806 is available in 10, 50 and 100-kohm versions and is specified over the industrial temperature
range. Packages for the device include 20-lead DIPs, SOICs, and TSSOPs.

OPERATION

A block diagram of the device is provided in Figure 1. As shown, the DS1806 contains six 64-position
potentiometers whose wiper positions are set by an 8-bit value. The DS1806 contains a 48-bit I/O shift
register which is used to store the respective wiper position data for each of the six potentiometers.

Each potentiometer has three terminals accessible to the user. These include the high side terminals, H

the wiper terminals, W

, and the low-end terminals, L1-3 and L4-6. Potentiometers 1 through 3 share the

same low-end terminal L1-3. And likewise, potentiometers 4 through 6 share the low-end terminal L4-6.

Control of the DS1806 is accomplished via a 3-wire serial communication interface which allows the user
to set the wiper position value for each potentiometer. The 3-wire serial interface consists of the control
signals

RST

, D

, and CLK. On power-up, the wiper positions of each potentiometer are set to the low-

end terminal L

(00000000).

The

RST

control signal is used to enable 3-wire serial port operation. The

RST

signal (3-wire serial port)

is active when in a high state. Any communication intended to change wiper settings must begin with the
transition of the

RST

from the low state to the high state.

The CLK signal input is used to provide timing synchronization for data input and output. Wiper position
data is loaded into the DS1806 through the D

input terminal. This data is shifted one bit at a time into

the 48-bit I/O shift register of the part, LSB first. Figure 3 provides an illustration of the 48-bit shift
register.

Figure 4 provides 3-wire serial port protocol and timing diagrams. As shown, the 3-wire port is inactive
when the

RST

signal input is low. Once

RST

has transitioned from the low to the high state, the serial

port becomes active. When active, data is loaded into the I/O shift register on the low-to-high transition of
the CLK.

Data is transmitted in order of LSB first. Potentiometers are designated from 1 through 6 and the value
for potentiometer-1 will be the first data entered into the shift register, followed by that of potentiometer-
2 and so forth.

Each wiper has an 8-bit register which is used for setting the position of the wiper on the resistor array.
Because the DS1806 is a 64-position potentiometer, only six bits of information are needed to set wiper
position. The remaining two bits of information are used to provide a "don't change" feature. Wiper
position is controlled by bit positions 0 through 5 of each register. The "don't change" feature is
controlled by bits 6 and 7 of each register. When bits 6 and 7 have value "11 xxxxxx," wiper position will
not change regardless of the states of bits 0 through 5. If bits 6 and 7 are set to any other value, bits 0
through 5 will be used as the new wiper position. The "don't change" feature allows the user to change
the value of any potentiometer of the DS1806 without affecting or having to remember the remaining
positions of the potentiometer wipers. Figure 2 provides the format for a wiper's register.

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Wiper placement for each potentiometer is such that position-63 corresponds to the H

terminal of the de-

vice while position-0 corresponds to the ground terminal. For example, to set a potentiometer's wiper
position to 15 (decimal), the binary value shifted into the wiper register should be 00001111. This will
place the wiper tap at the 15

step above the low-end terminal, L

All communication transactions should provide the total 48 bits of information when writing or reading
from the part. This is especially true for applications using all six potentiometers. If a complete set of 48
bits is not transmitted to the part, undesired wiper position settings may occur.

DS1806 BLOCK DIAGRAM Figure 1

WIPER REGISTER CONFIGURATION Figure 2

48-BIT I/O SHIFT REGISTER Figure 3

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3-WIRE SERIAL PORT TIMING Figure 4

CASCADE OPERATION

A feature of the DS1806 is the ability to control multiple devices from a single processor. Multiple
DS1806s can be linked or daisy chained as shown in Figure 5. As a data bit is entered into the I/O shift
register of the DS1806, a bit will appear at the C

OUT

terminal before a maximum delay of 50 nanoseconds.

The LSB of potentiometer-1 will always be the first out of the part at the beginning of a transaction.
Additionally, the C

OUT

terminal is always active regardless of the state

RST

. However, D

and CLK

inputs are ignored when

RST

is in the low state.

The C

OUT

output of the DS1806 can be used to drive the D

input of another DS1806. When cascading

multiple devices, the total number of bits transmitted is always 48 multiplied by the total number of
DS1806s being cascaded.

An optional feedback resistor can be placed between the C

OUT

terminal of the last device and the first

DS1806 D

input, which allows the controlling processor to read as well as write data or circularly clock

data through the daisy chain. The value of the feedback or isolation resistor should be in the range from 1
k

to 10 k

To read data, the reading device configures itself as an input and monitors the state of the D

line, which

is driven by C

OUT

through the isolation resistor. When

RST

is driven high, bit 48 is present on the C

OUT

pin, which is fed back to the input D

pin through the isolation resistor. When the CLK input transitions

low to high, bit 48 is loaded into the first position of the I/O shift register and bit 47 becomes present on
C

OUT

and D

of the next device. After 48 bits (or 48 times the number of the DS1806s in the daisy

chain), the data has shifted completely around and back to its original position. When

RST

transitions to

the low state to end data transfer, the value (the same as before the read occurred) is loaded in the shift
register.

ABSOLUTE AND RELATIVE LINEARITY

Absolute linearity is defined as the difference between the actual measured output voltage and the
expected output voltage. Absolute linearity is given in terms of a minimum increment or expected output
when the wiper is moved one position. The DS1806 is specified to have an absolute linearity of

0.50

LSB.

Relative linearity is a measure of error between two adjacent wiper position points. The DS1806 is
specified to have a relative linearity of

0.25 LSB.

Part Number DS1806