Philips Semiconductors

Product data

87LPC767

Low power, low price, low pin count (20 pin)

microcontroller with 4-kbyte OTP and 8-bit A/D converter

2001 Aug 07

11

Code Examples for the A/D

The first piece of sample code shows an example of port configuration for use with the A/D. This example sets up the pins so that all four A/D

channels may be used. Port configuration for analog functions is described in the section Analog Functions.

; Set up port pins for A/D conversion, without affecting other pins.

mov

PT0AD,#78h

; Disable digital inputs on A/D input pins.

anl

P0M2,#87h

; Disable digital outputs on A/D input pins.

orl

P0M1,#78h

; Disable digital outputs on A/D input pins.

Following is an example of using the A/D with interrupts. The routine ADStart begins an A/D conversion using the A/D channel number supplied

in the accumulator. The channel number is not checked for validity. The A/D must previously have been enabled with sufficient time to allow for

stabilization.

The interrupt handler routine reads the conversion value and returns it in memory address ADResult. The interrupt should be enabled prior to

starting the conversion.

; Start A/D conversion.

ADStart:

orl

ADCON,A

; Add in the new channel number.

setb

ADCS

; Start an A/D conversion.

;

orl

PCON,#01h

; The CPU could be put into Idle mode here.

;

orl

PCON,#02h

; The CPU could be put into Power Down mode here if RCCLK = 1.

ret

; A/D interrupt handler.

ADInt:

push

ACC

; Save accumulator.

mov

A,DAC0

; Get A/D result,

mov

ADResult,A

;

and save it in memory.

clr

ADCI

; Clear the A/D completion flag.

anl

ADCON,#0fch

; Clear the A/D channel number.

pop

ACC

; Restore accumulator.

reti

Following is an example of using the A/D with polling. An A/D conversion is started using the channel number supplied in the accumulator. The

channel number is not checked for validity. The A/D must previously have been enabled with sufficient time to allow for stabilization. The

conversion result is returned in the accumulator.

ADRead:

orl

ADCON,A

; Add in the new channel number.

setb

ADCS

; Start A/D conversion.

ADChk:

jnb

ADCI,ADChk

; Wait for ADCI to be set.

mov

A,DAC0

; Get A/D result.

clr

ADCI

; Clear the A/D completion flag.

anl

ADCON,#0fch

; Clear the A/D channel number.

ret