DS1803 Datasheet, PDF (4/11 Pages) Dallas Semiconductor – Addressable Dual Digital Potentiometer

DS1803
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.
SLAVE ADDRESS
A control byte is the first byte received following the START condition from the master device. The
control byte consist of a four bit control code; for the DS1803, this is set as 0101 binary for read/write
operations. 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 eight devices are to be accessed. The select bits are in effect the
three least significant bits of the slave address. Additionally, A2, A1 and A0 can be changed anytime
during a powered condition of the part. 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 structure for the DS1803.
Following the START condition, the DS1803 monitors the SDA bus checking the device type identifier
being transmitted. Upon receiving the 0101 address code and appropriate device select bits, the slave
device 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. Potentiometer data values and
control and command values are always transmitted most significant bit (MSB) first. During
communications 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
read/write 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. Again the flow of the read operation is presented in Figure 4.
Writing the DS1803
A data flow diagram for writing the DS1803 is shown in Figure 5. The DS1803 has three write command
operations. 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,
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