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
X
,
the wiper terminals, W
X
, 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
IN
, and CLK. On power-up, the wiper positions of each potentiometer are set to the low-
end terminal L
X
(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
IN
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.
