DS1307 Datasheet, PDF (7/11 Pages) Dallas Semiconductor – 64 X 8 Serial Real Time Clock

The DS1307 may operate in the following two modes:
DS1307
1. Slave receiver mode (DS1307 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 (See Figure 6). The address byte is
the first byte received after the start condition is generated by the master. The address byte contains
the 7 bit DS1307 address, which is 1101000, followed by the *direction bit (R/ W ) which, for a write,
is a 0. After receiving and decoding the address byte the device outputs an acknowledge on the SDA
line. After the DS1307 acknowledges the slave address + write bit, the master transmits a register
address to the DS1307 This will set the register pointer on the DS1307. The master will then begin
transmitting each byte of data with the DS1307 acknowledging each byte received. The master will
generate a stop condition to terminate the data write.
DATA WRITE - SLAVE RECEIVER MODE Figure 6
2. Slave transmitter mode (DS1307 read 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 DS1307 while the serial clock is input on SCL.
START and STOP conditions are recognized as the beginning and end of a serial transfer (See
Figure 7). The address byte is the first byte received after the start condition is generated by the
master. The address byte contains the 7-bit DS1307 address, which is 1101000, followed by the
*direction bit (R/ W ) which, for a read, is a 1. After receiving and decoding the address byte the
device inputs an acknowledge on the SDA line. The DS1307 then begins to transmit data starting
with the register address pointed to by the register pointer. If the register pointer is not written to
before the initiation of a read mode the first address that is read is the last one stored in the register
pointer. The DS1307 must receive a Not Acknowledge to end a read.
DATA READ - SLAVE TRANSMITTER MODE Figure 7
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