DS1807

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1. Data transfer from a master transmitter to a slave receiver. The first byte transmitted by the

master is the control byte (or 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 DS1807 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 DS1807 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 consists of a 4-bit control code. For the DS1807, this is set as 0101 binary for read/write

operations. The next 3 bits of the control byte are the device select bits (A2, A1, and 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. The last bit of the 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. Figure 5 shows the control byte structure for the DS1807.

Following the START condition, the DS1807 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 DS1807 allows the user to read or write the potentiometer(s).

The command structures for the part are presented in Figures 6 and 7. Potentiometer data values and

control and command values are always transmitted most significant bit (MSB) first. During

communications, the receiving unit always generates the acknowledgement.

READING THE DS1807

As shown in Figure 6, the DS1807 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 DS1807 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 DS1807, 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 DS1807.