DS1803
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DEVICE OPERATION
The DS1803 is an addressable, digitally controlled device which has two 256-position potentiometers. A
functional block diagram of the part is shown in Figure 1. Communication and control of the device is
accomplished via a 2-wire serial interface having signals SDA and SDL. Device addressing is attained
using the device chip select inputs A0, A1, A2 and correct communication protocol over the 2-wire serial
interface.
Each potentiometer is composed of a 256 position resistor array. Two 8-bit registers, each assigned to a
respective potentiometer, are used to set wiper position on the resistor array. The wiper terminal is
multiplexed to one of 256 positions on the resistor array based on its corresponding 8-bit register value.
For example, the high-end terminals, H0 and H1, have wiper position values FF(Hex) while the low-end
terminals, L0 and L1, have wiper position values 00(Hex).
The DS1803 is a volatile device that does not maintain the position of the wiper during power-down or
loss of power. On power-up, the DS1803 wipers’ position will be set to position 00(Hex) - the low-end
terminals. The user may then reset the wiper value to a desired position.
Communication with the DS1803 takes place over the 2-wire serial interface consisting of the bi-
directional data terminal, SDA, and the serial clock input, SCL. Complete details of the 2-wire interface
are discussed in the section entitled “2-wire Serial Bus.”
The 2-wire interface and chip select inputs A0, A1, and A2 allow operation of up to eight devices in a bus
topology; with A0, A1, and A2 being the address of the device.
Application Considerations
The DS1803 is offered in three standard resistor values which include the 10kΩ, 50kΩ, and 100kΩ. The
resolution of the potentiometer is defined as R
TOT
/255, where R
TOT
is the total resistor value of the
potentiometer. The DS1803 is designed to operate using 3V or 5V power supplies over the industrial
(-40°C to +85°C) temperature range. Maximum input signal levels across the potentiometer cannot
exceed the operating power supply of the device.
2-WIRE SERIAL DATA BUS
The DS1803 supports a bi-directional 2-wire bus and data transmission protocol. A device that sends data
on the bus is defined as a transmitter, and a device receiving data as a receiver. The device that controls
the message is called a “master”. The devices that are controlled by the master are “slaves”. The bus must
be controlled by a master device which generates the serial clock (SCL), controls the bus access, and
generates the START and STOP conditions. The DS1803 operates as a slave on the 2-wire bus.
Connections to the bus are made via the open-drain I/O lines SDA and SCL.
The following bus protocol has been defined (see Figure 2).
§ Data transfer may be initiated only when the bus is not busy.
§ During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in
the data line while the clock line is high will be interpreted as control signals.
Accordingly, the following bus conditions have been defined:
Bus not busy: Both data and clock lines remain HIGH.
