P80C550 查看數據表（PDF） - Philips Electronics

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P80C550

80C51 8-bit microcontroller family 4K/128 OTP/ROM/ROMless, 8 channel 8 bit A/D, watchdog timer

Philips Electronics 

Philips Semiconductors

80C51 8-bit microcontroller family

4K/128 OTP/ROM/ROMless, 8 channel 8 bit A/D, watchdog timer

Product specification

80C550/83C550/87C550

Sample A/D Routines

The following routines demonstrate two methods of operating the

A/D converter. The first method uses polling to determine when the

A/D conversion is complete. The second method uses the A/D

interrupt to flag the end of conversion.

The routine ReadAD will start a read of the A/D channel identified by

R7, and wait for the conversion to complete, polling the A/D interrupt

flag. The result is returned in the accumulator.

ReadAD:MOV A,#08h

;Basic A/D start command.

ORL A,R7

;Add channel # to be read.

MOV ADCON,A; ;Start A/D.

ADLoop: MOV A,ADCON ;Get A/D status.

JNB ACC.4,ADLoop;Wait for ADCI (A/D ;finished).

MOV A,ADAT

;Get conversion result

MOV ADCON,#0 ;Clear ADCI.

RET

The routine StartAD will start a read of the A/D channel identified by

R7 and exit back to the calling program. When the conversion is

complete, the A/D interrupt occurs, calling the A/D interrupt service

routine. The result of the conversion is returned in register R6.

StartAD: MOV A,#08h

ORL A,R7

MOV ADCON,A

RET

.

.

.

ORG 2Bh

ADInt: MOV R6,ADAT

MOV ADCON,#0

RETI

;Basic A/D start command.

;Add channel # to be read.

;Start A/D.

;A/D interrupt address.

;Get conversion result.

;Clear ADCI.

IN+1

SmN+1 RmN+1

SmN

RmN

IN

To Comparator

+

Multiplexer

RS

VANALOG

CS

CC

INPUT

Rm = 0.5 - 3 kΩ

CS + CC = 15pF maximum

RS = Recommended < 9.6 kΩ for 1 LSB @ 12MHz

NOTE:

Because the analog to digital converter has a sampled-data comparator, the input looks capacitive to a source. When a conversion

is initiated, switch Sm closes for 8tcy (8µs @ 12MHz crystal frequency) during which time capacitance Cs + Cc is charged. It should

be noted that the sampling causes the analog input to present a varying load to an analog source.

Figure 3. A/D Input: Equivalent Circuit

SU00199

1998 May 01

9

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