DS1808

6 of 17

The master device generates all 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 DS1808 may operate in the following two modes:

1. Slave receiver mode: Serial data and clock are received through SDA and SCL respectively. 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 (device) 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 DS1808 while the serial clock is input on SCL. Start and stop conditions

are recognized as the beginning and end of a serial transfer.

3. Slave Address: command/control byte is the first byte received following the start condition from the

master device. The command/control byte consists of a 4-bit control code. For the DS1808, this is set

as 0101 binary for read/write operations. The next three bits of the command/control byte are the

device select bits or slave address (A2, A1, A0). They are used by the master device to select which

of eight devices is to be accessed. When reading or writing the DS1808, the device select bits must

match the device select pins (A2, A1, A0). The last bit of the command/control byte (R/W) defines

the operation to be performed. When set to a 1, a read operation is selected, and when set to a 0, a

write operation is selected.

Following the START condition, the DS1808 monitors the SDA bus checking the device type identifier

being transmitted. Upon receiving the 0101 control code, the appropriate device address bits, and the

read/write bit, the slave device outputs an acknowledge signal on the SDA line.

COMMAND AND PROTOCOL

The command and protocol structure of the DS1808 allows the user to read from or write to the

potentiometer(s). Additionally, the 2-wire command/protocol structure of the DS1808 will support eight

different devices and a maximum of 16 channels that can be uniquely controlled. The command

structures for the device are presented in Figures 3, 4, 5, and 6. Potentiometer data values and

command/control values are always transmitted most significant bit (MSB) first. During communications,

the receiving unit always generates the acknowledgement.