DS1337 Datasheet, PDF (12/13 Pages) Dallas Semiconductor – Serial Real-Time Clock

Figure 4. Data Transfer On 2-Wire Serial Bus
DS1337
Depending upon the state of the R/W bit, two types of data transfer are possible:
1) Data transfer from a master transmitter to a slave receiver. The first 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 is transferred with the most significant bit (MSB) first.
2) Data transfer from a slave transmitter to a master receiver. The master transmits the first byte
(the slave address). The slave then returns an acknowledge bit, followed by the slave transmitting a
number of data bytes. 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 is not released. Data is transferred with the most
significant bit (MSB) first.
The DS1337 can operate in the following two modes:
1) Slave Receiver Mode (Write 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 (Figure 5). The slave address byte is
the first byte received after the master generates the START condition. The slave address byte
contains the 7-bit DS1337 address, which is 1101000, followed by the direction bit (R/W), which, for
a write, is 0. After receiving and decoding the slave address byte the device outputs an acknowledge
on the SDA line. After the DS1337 acknowledges the slave address + write bit, the master transmits a
word address to the DS1337. This sets the register pointer on the DS1337. The master may then
transmit 0 or more bytes of data, with the DS1337 acknowledging each byte received. The master
generates a STOP condition to terminate the data write.
2) Slave Transmitter Mode (Read Mode): The first byte is received and handled as in the slave
receiver mode. However, in this mode, the direction bit indicates that the transfer direction is
reversed. Serial data is transmitted on SDA by the DS1337 while the serial clock is input on SCL.
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