Application Note

DS1307 Software Interface

AN1759

11

Data Write

Sequence

The first byte transmitted in a write to the DS1307 is its 7-bit identification

code followed by the R/W bit. For writes, this bit will be 0. The next byte

transmitted is the DS1307 address pointer. After this, bytes of data to be

written to the DS1307 RAM are transmitted. After each byte of data is

written, the address pointer is incremented. See Figure 9.

Figure 9. Data Write Sequence

Data Read

Sequence

The first byte transmitted in a read from the DS1307 is its 7-bit

identification code followed by the R/W bit. For reads, this bit will be 1.

Then the DS1307 will begin transmitting data back to the master. As long

as the DS1307 receives clocks and acknowledgments, it keeps

transmitting data. The starting address is the previous address pointer

from the last write transaction. If needed, a write sequence with only an

address can be used to initialize the address pointer for reads.

NOTE:

Remember that for the last byte read, the master sends back a No ACK

to the DS1307.

Figure 10. Data Read Sequence

START

1101000

DS1307 ADDRESSR/W

0 ACK

XXXX,XXXX

ADDRESS POINTER

ACK

XXXX,XXXX

DATA (N)

ACK

XXXX,XXXX

DATA (N+?)

ACK

STOP

START

1101000

DS1307 ADDRESS R/W

1 ACK

XXXX,XXXX

DATA (N)

ACK

XXXX,XXXX

DATA (N+?)

ACK STOP

Freescale Semiconductor, Inc.

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