AT87C5111-ICSIL datasheet(54/86 Pages) ATMEL

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AT8xC5111

4190A–8051–11/02

Analog-to-Digital

Converter (ADC)

This section describes the on-chip 10-bit analog-to-digital converter of the

T89C51RB2/RC2. Eight ADC channels are available for sampling of the external

sources AN0 to AN7. An analog multiplexer allows the single ADC to select one of the 8

ADC channels as ADC input voltage (ADCIN). ADCIN is converted by the 10 bit-cas-

caded potentiometric ADC.

Three kind of conversions are available:

•

Standard conversion (7-8 bits).

•

Precision conversion (8-9 bits).

•

Accurate conversion (10 bits).

For the precision conversion, set bits PSIDLE and ADSST in ADCON register to start

the conversion. The chip is in a pseudo-idle mode, the CPU doesn’t run but the periph-

erals are always running. This mode allows digital noise to be lower, to ensure precise

conversion.

For the accurate conversion, set bits QUIETM and ADSST in ADCON register to start

the conversion. The chip is in a quiet mode, the AD is the only peripheral running. This

mode allows digital noise to be as low as possible, to ensure high precision conversion.

For these modes 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.

Features

•

8 channels with multiplexed inputs

•

10-bit cascaded potentiometric ADC

•

Conversion time down to 10 micro-seconds

•

Zero Error (offset) ± 2 LSB max

•

External Positive Reference Voltage Range 2.4 to V

•

ADCIN Range 0 to V

•

Integral non-linearity typical 1 LSB, max. 2 LSB (with 0.9*V

CC<VREF<VCC)

•

Differential non-linearity typical 0.5 LSB, max. 1 LSB (with 0.9*V

CC<VREF<VCC)

•

Conversion Complete Flag or Conversion Complete Interrupt

•

Selected ADC Clock

ADC I/O Functions

AINx are general I/Os that are shared with the ADC channels. The channel select bits in

ADCF register define which ADC channel pin will be used as ADCIN. The remaining

ADC channels pins can be used as general purpose I/Os 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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