Philips Semiconductors
Product specification
LCD direct/duplex driver with
I2C-bus interface
PCF8577C
CHARACTERISTICS OF THE I2C-BUS
7.4
Acknowledge
7
The I2C-bus is for 2-way, 2-line communication between
different ICs or modules. The two lines are a serial data
line (SDA) and a serial clock line (SCL). Both lines must be
connected to a positive supply via a pull-up resistor when
connected to the output stages of a device. Data transfer
may be initiated only when the I2C-bus is not busy.
The number of data bytes transferred between the start
and stop conditions from transmitter to receiver is not
limited. Each byte is followed by one acknowledge bit.
The acknowledge bit is a HIGH level put on the I2C-bus by
the transmitter whereas the master generates an extra
acknowledge related clock pulse. A slave receiver which is
addressed must generate an acknowledge after the
reception of each byte. Also a master must generate an
acknowledge after the reception of each byte that has
been clocked out of the slave transmitter. The device that
acknowledges has to pull down the SDA line during the
acknowledge clock pulse, set-up and hold times must be
taken into account. A master receiver must signal an end
of data to the transmitter by not generating an
7.1
Bit transfer
One data bit is transferred during each clock pulse.
The data on the SDA line must remain stable during the
HIGH period of the clock pulse as changes in the data line
at this time will be interpreted as control signals.
7.2
Start and stop conditions
acknowledge on the last byte that has been clocked out of
the slave. In this event the transmitter must leave the data
line HIGH to enable the master to generate a stop
condition.
Both data and clock lines remain HIGH when the I2C-bus
is not busy. A HIGH-to-LOW transition of the data line,
while the clock is HIGH is defined as the start condition (S).
A LOW-to-HIGH transition of the data line while the clock
is HIGH is defined as the stop condition (P).
7.3
System configuration
A device generating a message is a ‘transmitter’, a device
receiving a message is the ‘receiver’. The device that
controls the message is the ‘master’ and the devices which
are controlled by the master are the ‘slaves’.
SDA
SCL
data line
stable;
data valid
change
of data
allowed
MBA607
Fig.8 Bit transfer.
1998 Jul 30
10
NXP [ NXP ]
