DS1307 64 x 8, Serial, I

2C Real-Time Clock

12 of 14

...

A

XXXXXXXX

A

1101000

S

0

XXXXXXXX

A XXXXXXXX

A

XXXXXXXX

A P

<Slave Address>

<Word Address (n)>

<Data(n)>

<Data(n+1)>

<Data(n+X)>

S - Start

A - Acknowledge (ACK)

P - Stop

DATA TRANSFERRED

(X+1 BYTES + ACKNOWLEDGE)

Master to slave

Slave to master

A

XXXXXXXX

A

1101000

S

1

XXXXXXXX

A XXXXXXXX

XXXXXXXX

A P

<Slave Address>

<Data(n)>

<Data(n+1)>

<Data(n+2)>

<Data(n+X)>

S - Start

A - Acknowledge (ACK)

P - Stop

A - Not Acknowledge (NACK)

DATA TRANSFERRED

(X+1 BYTES + ACKNOWLEDGE); NOTE: LAST DATA BYTE IS

FOLLOWED BY A NOT ACKNOWLEDGE (

A) SIGNAL)

Master to slave

Slave to master

...

A

The DS1307 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. Hardware performs address recognition after reception of

the slave address and direction bit (see Figure 4). The slave address byte is the first byte received

after the master generates the START condition. The slave address byte contains the 7-bit DS1307

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 DS1307 outputs an acknowledge on SDA. After the DS1307

acknowledges the slave address + write bit, the master transmits a word address to the DS1307. This

sets the register pointer on the DS1307, with the DS1307 acknowledging the transfer. The master can

then transmit zero or more bytes of data with the DS1307 acknowledging each byte received. The

register pointer automatically increments after each data byte are written. The master will generate 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 will indicate that the transfer direction is reversed. The

DS1307 transmits serial data on SDA 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 5). 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 DS1307 address, which is 1101000, followed by the direction bit (R/

W),

which is 1 for a read. After receiving and decoding the slave address the DS1307 outputs an

acknowledge on SDA. 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 register pointer

automatically increments after each byte are read. The DS1307 must receive a Not Acknowledge to

end a read.

Figure 4. Data Write—Slave Receiver Mode

Figure 5. Data Read—Slave Transmitter Mode