PCF8820 datasheet(17/60 Pages) PHILIPS

17 / 60 page

2000 Dec 07

Philips Semiconductors

Product speciﬁcation

× 101 Grey-scale/ECB colour dot matrix

LCD driver

PCF8820

7.18.5

I2C-BUS PROTOCOL

The PCF8820 is a slave transmitter/receiver. If data is to

be read from the device, the SDA_OUT output must be

used.

Before any data is transferred over the I2C-bus, the

destination device is addressed first (see Fig.15).

The PCF8820 has four 7-bit slave addresses reserved:

0111 100, 0111 101, 0111 110 and 0111 111. The two

least significant bits of the slave address are set by

connecting slave address inputs SA1 and SA0 to either

VSS1 (logic 0) or VDD1 (logic 1).

A write sequence (see Fig.17) is initiated with a START

condition (S) from the I2C-bus master which is followed by

the slave address. Only the addressed slave

acknowledges. After acknowledgement, one or more

command words follow which define the status of the

addressed slave.

A command word consists of a control byte (see Fig.16)

defining ‘continuation’ bit Co and ‘register selection’

bit RS, plus a data byte. The last control byte is indicated

by resetting bit Co = 0. The control and data bytes are also

acknowledged by all addressed slaves on the bus.

Depending on the setting of bit RS in the last control byte,

either a series of display data bytes or command data

bytes may follow.

If bit RS = 1, the data bytes are stored as display data in

the DDRAM at the address specified by the data pointer.

The data pointer is automatically incremented.

If bit RS = 0, the data byte is interpreted as a command

byte to be decoded and the device will be set according to

the received commands.

Only the addressed PCF8820 acknowledges after each

byte is received. The I2C-bus master issues a stop

condition (P) at the end of the transmission.

MGU185

01111

SA0

SA1

slave address

R/W

acknowledge

bit

START

condition

slave

address

bit 1

read/write

bit

slave

address

bit 0

Fig.15 Slave address.

MGT124

XXXXXX

control byte

selection

bit

continuation

bit

Fig.16 Control byte.

handbook, full pagewidth

MGT125

S 01111

acknowledgement

from PCF8820

acknowledgement

from PCF8820

acknowledgement

from PCF8820

acknowledgement

from PCF8820

acknowledgement

from PCF8820

control byte

data byte

≥ 0 bytes

1 byte

slave address

≥ 0 bytes

update

data pointer

A P

R/W

control byte

Fig.17 Write sequence: master transmits bytes to slave receiver.

PCF8820 Datasheet(PDF) 17 Page - NXP Semiconductors

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