DS1721U Datasheet, PDF (8/17 Pages) Maxim Integrated Products – 2-Wire Digital Thermometer and Thermostat

DATA TRANSFER ON 2-WIRE SERIAL BUS Figure 5
DS1721
Figure 6 details how data transfer is accomplished on the two-wire bus. Depending upon the state of the
R/ W bit, two types of data transfer are possible:
Data transfer from a master transmitter to a slave receiver. The 1^st byte transmitted by the master is
the slave address. Next follows a number of data bytes. The slave returns an acknowledge bit after each
received byte.
Data transfer from a slave transmitter to a master receiver. The 1^st 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 DS1721 may operate in the following two modes:
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.
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 DS1721 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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