STFPC320 datasheet(23/78 Pages) STMICROELECTRONICS

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STFPC320

Real-time clock (RTC) operation

23/78

condition. The number of data bytes transferred between the start and stop conditions

is not limited. The information is transmitted byte-wide and each receiver acknowledges

with a ninth bit.

By definition a device that gives out a message is called “transmitter,” the receiving

device that gets the message is called “receiver.” The device that controls the message

is called “master.” The devices that are controlled by the master are called “slaves.”

●

Acknowledge: each byte of eight bits is followed by one Acknowledge Bit. This

Acknowledge Bit is a low level put on the bus by the receiver whereas the master

generates an extra acknowledge related clock pulse. A slave receiver which is

addressed is obliged to generate an acknowledge after the reception of each byte that

has been clocked out of the master transmitter.

The device that acknowledges has to pull down the SDA line during the acknowledge

clock pulse in such a way that the SDA line is a stable Low during the High period of the

acknowledge related clock pulse. Of course, setup and hold times must be taken into

account. A master receiver must signal an end of data to the slave transmitter by not

generating an acknowledge on the last byte that has been clocked out of the slave. In

this case the transmitter must leave the data line High to enable the master to generate

the STOP condition.

Figure 9.

Serial bus data transfer sequence

Figure 10.

Acknowledgement sequence

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