PCF2104CUSLASH2 datasheet(24/56 Pages) MOTOROLA

24 / 56 page

1997 Dec 16

Philips Semiconductors

Product speciﬁcation

LCD controller/driver

PCF2104x

11 INTERFACE TO MICROCONTROLLER

(I2C-BUS INTERFACE)

11.1

Characteristics of the I2C-bus

The I2C-bus is for bidirectional, two-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. Data transfer may be initiated only when

the bus is not busy.

11.2

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 a control signal.

11.3

Start and stop conditions

Both data and clock lines remain HIGH when the 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).

11.4

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’.

11.5

Acknowledge

The number of data bytes transferred between the start

and stop conditions from transmitter to receiver is

unlimited. Each byte of eight bits is followed by an

acknowledge bit. The acknowledge bit is a HIGH level

signal put on the bus by the transmitter during which time

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 receiver must generate an acknowledge after the

reception of each byte that has been clocked out of the

slave transmitter. The device that acknowledges must

pull-down the SDA line during the acknowledge clock

pulse, so that the SDA line is stable LOW during the HIGH

period of the acknowledge related clock pulse (set-up and

hold times must be taken into consideration). A master

receiver must signal an end of data to the transmitter by

not generating an 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.

11.6

I2C-bus protocol

Before any data is transmitted on the I2C-bus, the device

which should respond is addressed first. The addressing is

always carried out with the first byte transmitted after the

start procedure. The I2C-bus configuration for the different

PCF2104x READ and WRITE cycles is illustrated in

Figs 22, 23 and 24.

Fig.18 Bit transfer.

handbook, full pagewidth

MBC621

data line

stable;

data valid

change

of data

allowed

SDA

SCL

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