Rainbow Electronics DS1339 - Manual (Page 13)

DS1339
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The DS1339 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 8). The slave address byte is
the first byte received after the START condition is generated by the master. The slave address byte
contains the 7-bit DS1339 address, which is 1101000, followed by the direction bit (R/
W ), which, for
a write, is a 0. After receiving and decoding the slave address byte, the slave outputs an acknowledge
on the SDA line. After the DS1339 acknowledges the slave address + write bit, the master transmits a
register address to the DS1339. This sets the register pointer on the DS1339, with the DS1339
acknowledging the transfer. The master can then transmit zero or more bytes of data, with the
DS1339 acknowledging each byte received. The address pointer increments after each byte is
transferred. 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 DS1339 while the serial clock is input on SCL.
START and STOP conditions are recognized as the beginning and end of a serial transfer (Figure 9).
The slave address byte is the first byte received after the START condition is generated by the
master. The slave address byte contains the 7-bit DS1339 address, which is 1101000, followed by the
direction bit (R/
W ), which, for a read, is a 1. After receiving and decoding the slave address byte the
slave outputs an acknowledge on the SDA line. The DS1339 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
address pointer is incremented after each byte is transferred. The DS1339 must receive a “not
acknowledge” to end a read.
Figure 8. DATA WRITE: SLAVE RECEIVER MODE
Figure 9. DATA READ: SLAVE TRANSMITTER MODE