DS1803
Addressable Dual Digital Potentiometer
www.maxim-ic.com
FEATURES
3V or 5V Operation
Ultra-Low Power Consumption
Two Digitally Controlled, 256-Position
Potentiometers
14-Pin TSSOP (173 mil) and 16-Pin SO (150
mil) Packaging Available for Surface-Mount
Applications
Addressable Using 3 Address Inputs
2-Wire Serial Interface
Operating Temperature Range:
- Industrial: -40°C to +85°C
Standard Resistance Values:
- DS1803-010
10kΩ
- DS1803-050
50kΩ
- DS1803-100
100kΩ
PIN ASSIGNMENT
H1
L1
W1
A2
A1
A0
GND
1
2
3
4
5
6
7
14
13
12
11
10
9
8
VCC
NC
H0
L0
W0
SDA
SCL
DS1803 14-PIN TSSOP (173 MIL)
H1
NC
L1
W1
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VCC
NC
H0
L0
W0
NC
SDA
SCL
PIN DESCRIPTION
L0, L1
H0, H1
W0,W1
V
CC
A0, A1, A2
SDA
SCL
GND
NC
-
-
-
-
-
-
-
-
-
Low End of Resistor
High End of Resistor
Wiper terminal of Resistor
3V/5V Power Supply Input
Chip Select Inputs
Serial Data I/O
Serial Clock Input
Ground
No Connection
A2
A1
A0
GND
DS1803Z 16-PIN SO (150 MIL)
DS1803 16-PIN DIP (300 MIL)
See Mech. Drawings Section on Website
DESCRIPTION
The DS1803 addressable dual digital potentiometer features two independently controlled 256-position
potentiometers. Device control is achieved through a 2-wire serial interface. Three address pins allow up
to 8 DS1803’s to share the same 2-wire interface. The exact wiper position of each potentiometer can be
written or read. The DS1803 is available in a 16-pin DIP, 16-pin SO, and 14-pin TSSOP package. The
device is available in three standard resistance values: 10kΩ, 50kΩ, and 100kΩ and is specified over the
industrial temperature range.
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DS1803
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. Address inputs A0, A1, and A2 allow up to 8 DS1803s to
share the same 2-wire 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 the 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 FFh while the low-end
terminals, L0 and L1, have wiper position values 00h.
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 00h - the low-end
terminals. The user may then set the wiper value to a desired position.
Communication with the DS1803 takes place over the 2-wire serial interface consisting of the bi-
directional pin, SDA, and the serial clock input, SCL. Complete details of the 2-wire interface are
discussed in the section entitled “2-wire Serial Data Bus.”
Application Considerations
The DS1803 is offered in three standard resistor values, which include 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.
Start data transfer:
A change in the state of the data line, from HIGH to LOW, while the clock is
HIGH, defines a START condition.
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DS1803
Stop data transfer:
A change in the state of the data line, from LOW to HIGH, while the clock line is
HIGH, defines the STOP condition.
Data valid:
The state of the data line represents valid data when, after a START condition, the data line
is stable for the duration of the HIGH period of the clock signal. The data on the line must be changed
during the LOW period of the clock signal. There is one clock pulse per bit of data. Figure 2 details how
data transfer is accomplished on the 2-wire bus. Depending upon the state of the R/
W
* bit, two types of
data transfer are possible.
Each data transfer is initiated with a START condition and terminated with a STOP condition. The
number of data bytes transferred between START and STOP conditions is not limited, and is determined
by the master device. The information is transferred byte-wise and each receiver acknowledges with a
ninth bit.
Acknowledge:
Each receiving device, when addressed, is obliged to generate an acknowledge after the
reception of each byte. The master device must generate an extra clock pulse which is associated with this
acknowledge bit.
A device that acknowledges must pull down the SDA line during the acknowledge clock pulse in such a
way that the SDA line is stable LOW during the HIGH period of the acknowledge related clock pulse. Of
course, setup and hold times must be taken into account. A master must signal an end of data to the slave
by not generating an acknowledge bit on the last byte that has been clocked out of the slave. In this case,
the slave must leave the data line HIGH to enable the master to generate the STOP condition.
1.
Data transfer from a master transmitter to a slave receiver:
The first byte transmitted by the
master is the control byte (slave address). Next follows a number of data bytes. The slave returns an
acknowledge bit after each received byte.
2.
Data transfer from a slave transmitter to a master receiver:
The first byte (the slave address) is
transmitted by the master. The slave then returns an acknowledge bit. Next follows a number of data
bytes transmitted by the slave to the master. The master returns an acknowledge bit after all received
bytes other than the last byte. At the end of the last received byte, a ‘not acknowledge’ is returned.
The master device generates all of the serial clock pulses and the START and STOP conditions. A
transfer is ended with a STOP condition or with a repeated START condition. Since a repeated START
condition is also the beginning of the next serial transfer, the bus will not be released.
The DS1803 may operate in the following two modes:
1.
Slave receiver mode:
Serial data and clock are received through SDA and SCL. After each byte is
received, an acknowledge bit is transmitted. START and STOP conditions are recognized as the
beginning and end of a serial transfer. Address recognition is performed by hardware after reception
of the slave address and direction bit.
2.
Slave transmitter mode:
The first byte is received and handled as in the slave receiver mode.
However, in this mode the direction bit will indicate that the transfer direction is reversed. Serial data
is transmitted on SDA by the DS1803 while the serial clock is input on SCL. START and STOP
conditions are recognized as the beginning and end of a serial transfer.
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DS1803
SLAVE ADDRESS
The control byte is the first byte received following the START condition from the master device. The
control byte consists of a four bit control code; for the DS1803, this is 0101 binary. The next three bits of
the control byte are the device select bits (A2, A1, A0). They are used by the master device to select
which of the devices on the bus are to be accessed. The last bit of the control byte (R/
W
*) defines the
operation to be performed. When set to a one a read operation is selected, and when set to a zero a write
operation is selected. Figure 3 shows the control byte for the DS1803.
Following the START condition, the DS1803 monitors the SDA bus for the control byte being
transmitted. Upon receiving a matching control byte, the DS1803 outputs an acknowledge signal on the
SDA line.
COMMAND AND PROTOCOL
The command and protocol structure of the DS1803 allows the user to read or write the potentiometer(s).
The command structures for the part are presented in Figures 4 and 5. Data is transmitted most significant
bit (MSB) first. During communication, the receiving unit always generates the acknowledge.
Reading the DS1803
As shown in Figure 4, the DS1803 provides one read command operation. This operation allows the user
to read both potentiometers. Specifically, the R/
W
bit of the control byte is set equal to a 1 for a read
operation. Communication to read the DS1803 begins with a START condition which is issued by the
master device. The control byte from the master device will follow the START condition. Once the
control byte has been received by the DS1803, the part will respond with an ACKNOWLEDGE. The
R/
W
bit of the control byte as stated should be set equal to ‘1’ for reading the DS1803.
When the master has received the ACKNOWLEDGE from the DS1803, the master can then begin to
receive potentiometer wiper data. The value of the potentiometer-0 wiper position will be the first
returned from the DS1803. Once the eight bits of the potentiometer-0 wiper position has been transmitted,
the master will need to issue an ACKNOWLEDGE, unless it is the only byte to be read, in which case the
master issues a NOT ACKNOWLEDGE. If desired the master may stop the communication transfer at
this point by issuing the STOP condition. However, if the value of the potentiometer-1 wiper position
value is needed, communication transfer can continue by clocking the remaining eight bits of the
potentiometer-1 value, followed by an NOT ACKNOWLEDGE. Final communication transfer is
terminated by issuing the STOP command.
Writing the DS1803
A data flow diagram for writing the DS1803 is shown in Figure 5. The DS1803 has three write
commands. These include write pot-0, write pot-1, and write pot-0/1. The write pot-0 command allows
the user to write the value of potentiometer-0 and as an option the value of potentiometer-1. The write-1
command allows the user to write the value of potentiometer-1 only. The last write command, write-0/1,
allows the user to write both potentiometers to the same value with one command and one data value
being issued.
All the write operations begin with a START condition. Following the START condition, the master
device will issue the control byte. The read/write bit of the control byte will be set to ‘0’ for writing the
DS1803. Once the control byte has been issued and the master receives the acknowledgment from the
DS1803, the command byte is transmitted to the DS1803. As mentioned above, there exist three write
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DS1803
operations that can be used with the DS1803. The binary value of each write command is shown in Figure
5 and also in the Table 1.
2-WIRE COMMAND WORDS
Table 1
COMMAND
Write Potentiometer-0
Write Potentiometer-1
Write Both Potentiometers
COMMAND VALUE
101010 01
101010 10
101011 11
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