P87LPC779 datasheet(13/74 Pages) PHILIPS

13 / 74 page

Philips Semiconductors

P87LPC779

CMOS single-chip 8-bit microcontroller

Product data

Rev. 02 — 03 May 2004

13 of 74

9397 750 13213

the A/D to stabilize. Prior to the beginning of an A/D conversion, one analog input pin

must be selected for conversion via the AADR1 and AADR0 bits. These bits cannot

be changed while the A/D is performing a conversion.

An A/D conversion is started by setting the ADCS bit, which remains set while the

conversion is in progress. When the conversion is complete, the ADCS bit is cleared

and the ADCI bit is set. When ADCI is set, it will generate an interrupt if the interrupt

system is enabled, the A/D interrupt is enabled (via the EAD bit in the IE1 register),

and the A/D interrupt is the highest priority pending interrupt.

When a conversion is complete, the result is contained in the register DAC0 and can

be read to get the ADC result. This value will not change until another conversion is

started. Before another A/D conversion may be started, the ADCI bit must be cleared

by software. The A/D channel selection may be changed by the same instruction that

sets ADCS to start a new conversion, but not by the same instruction that clears

ADCI.

The connections of the A/D converter are shown in Figure 5.

The ideal A/D result may be calculated as follows:

(1)

Table 4:

ADCON - A/D control register (address C0h) bit allocation

Bit addressable; Reset value: 00H

Bit

Symbol

ENADC

DAC1

DAC0

ADCI

ADCS

RCCLK

AADR1

AADR0

Table 5:

ADCON - A/D control register (address C0h) bit description

Bit

Symbol

Description

ENADC

When ENADC = 1, the A/D is enabled and conversions may take

place. Must be set 10 microseconds before a conversion is started.

ENADC cannot be cleared while ADCS or ADCI are ‘1’.

DAC1

When ENDAC1 = 1, DAC1 is enabled to provide an analog output

voltage. Refer to Section 8.5 “Digital to Analog Converter (DAC)

outputs” on page 17.

DAC0

When ENDAC1 = 0, DAC0 is enabled to provide an analog output

voltage. Writable while ADCS and ADCI are ‘0’. Refer to Section

8.5 “Digital to Analog Converter (DAC) outputs” on page 17 for

more detail. ENADC and ENDAC0 should not be set at the same

time.

Result

–

()

256

–

-------------------------- round result to the nearest integer

()

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