PCF8591T datasheet(5/28 Pages) PHILIPS

5 / 28 page

2003 Jan 27

Philips Semiconductors

Product speciﬁcation

8-bit A/D and D/A converter

PCF8591

FUNCTIONAL DESCRIPTION

7.1

Addressing

Each PCF8591 device in an I2C-bus system is activated by

sending a valid address to the device. The address

consists of a fixed part and a programmable part. The

programmable part must be set according to the address

pins A0, A1 and A2. The address always has to be sent as

the first byte after the start condition in the I2C-bus

protocol. The last bit of the address byte is the

read/write-bit which sets the direction of the following data

transfer (see Figs 4, 16 and 17).

7.2

Control byte

The second byte sent to a PCF8591 device will be stored

in its control register and is required to control the device

function. The upper nibble of the control register is used for

enabling the analog output, and for programming the

analog inputs as single-ended or differential inputs. The

lower nibble selects one of the analog input channels

defined by the upper nibble (see Fig.5). If the

auto-increment flag is set, the channel number is

incremented automatically after each A/D conversion.

If the auto-increment mode is desired in applications

where the internal oscillator is used, the analog output

enable flag in the control byte (bit 6) should be set. This

allows the internal oscillator to run continuously, thereby

preventing conversion errors resulting from oscillator

start-up delay. The analog output enable flag may be reset

at other times to reduce quiescent power consumption.

The selection of a non-existing input channel results in the

highest available channel number being allocated.

Therefore, if the auto-increment flag is set, the next

selected channel will be always channel 0. The most

significant bits of both nibbles are reserved for future

functions and have to be set to logic 0. After a Power-on

reset condition all bits of the control register are reset to

logic 0. The D/A converter and the oscillator are disabled

for power saving. The analog output is switched to a

high-impedance state.

handbook, halfpage

MBL823

AIN0

AIN1

AIN2

AIN3

VSS

VDD

AOUT

VREF

AGND

EXT

OSC

SCL

SDA

PCF8591T

Fig.3 Pinning diagram (SO16).

handbook, halfpage

MBL824

msb

lsb

fixed part

programmable part

R/W

Fig.4 Address byte.

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