T89C51AC2-RLSI-M datasheet(87/117 Pages) ATMEL

87 / 117 page

Draft.A - March 30, 2001

Preview - Confidential

T89C51AC2

16. Analog-to-Digital Converter (ADC)

16.1. Introduction

This section describes the on-chip 10 bit analog-to-digital converter of the T89C51AC2. Eight ADC channels are

available for sampling of the external sources AN0 to AN7. An analog multiplexer allows the single ADC converter

to select one from the 8 ADC channels as ADC input voltage (ADCIN). ADCIN is converted by the 10 bit-

cascaded potentiometric ADC.

Two kind of conversion are available:

- Standard conversion (8 bits).

- Precision conversion (10 bits).

For the precision conversion, set bit PSIDLE in ADCON register and start conversion. The chip is in a pseudo-

idle mode, the CPU doesn’t run but the peripherals are always running. This mode allows digital noise to be as

low as possible, to ensure high precision conversion.

For this mode it is necessary to work with end of conversion interrupt, which is the only way to wake up the chip.

If another interrupt occurs during the precision conversion, it will be treated only after this conversion is ended.

16.2. Features

• 8 channels with multiplexed inputs

• 10-bit cascaded potentiometric ADC

• Conversion time 20 micro-seconds

• Zero Error (offset) +/- 2 LSB max

• Positive Reference Voltage Range 2.4 to 3.0Volt

• ADCIN Range 0 to 3Volt

• Integral non-linearity typical 1 LSB, max. 2 LSB

• Differential non-linearity typical 0.5 LSB, max. 1 LSB

• Conversion Complete Flag or Conversion Complete Interrupt

• Selected ADC Clock

16.3. ADC Port1 I/O Functions

Port 1 pins are general I/O that are shared with the ADC channels. The channel select bit in ADCF register define

which ADC channel/port1 pin will be used as ADCIN. The remaining ADC channels/port1 pins can be used as

general purpose I/O or as the alternate function that is available. Writes to the port register which aren’t selected

by the ADCF will not have any effect.

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