PCF8591 datasheet(6/28 Pages) PHILIPS

6 / 28 page

1998 Jul 02

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 3, 15 and 16).

Fig.3 Address byte.

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.4). 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 0. After a Power-on reset

condition all bits of the control register are reset to 0.

The D/A converter and the oscillator are disabled for power

saving. The analog output is switched to a high-impedance

state.

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