DS1339 I2C Serial Real-Time Clock
data, with the DS1339 acknowledging each byte received. The address pointer increments after each data
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 10). 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 is 1 for a read. 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 9. Data Write—Slave Receiver Mode
slave address
1101000
register address (n)
Data (n)
Data (n+1)
Data (n+x)
S
0
A
A
A
A
P
XXXXXXXX
XXXXXXXX
XXXXXXXX
XXXXXXXX
S - START
A - ACKNOWLEDGE
P - STOP
DATA TRANSFERRED
(X+1 BYTES + ACKNOWLEDGE)
R/W - READ/WRITE OR DIRECTION BIT
Figure 10. Data Read—Slave Transmitter Mode
slave address
1101000
Data (n)
Data (n+1)
Data (n+2)
Data (n+x)
XXXXXXXX
S
1
A
A
A
A
/A
S - START
A - ACKNOWLEDGE
P - STOP
DATA TRANSFERRED
(X+1 BYTES + ACKNOWLEDGE)
/A - NOT ACKNOWLEDGE
R/W - READ/WRITE OR DIRECTION BIT
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DALLAS [ DALLAS SEMICONDUCTOR ]
