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T89C51AC2

Rev. B – 19-Dec-01

16. Analog-to-Digital

Converter (ADC)

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 chan-

nels 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 device is in a pseudo-idle mode, the CPU does not 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 the device up.

If another interrupt occurs during the precision conversion, it will be treated only after

this conversion is ended.

16.1 Features • 8 channels with multiplexed inputs

• 10-bit cascaded potentiometric ADC

• Conversion time 16 micro-seconds (typ.)

• Zero Error (offset) +/- 2 LSB max

• Positive External Reference Voltage Range (VREF) 2.4 to 3.0Volt (typ.)

• ADCINRange0to3Volt

• 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

• Selectable ADC Clock

16.2 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 alter-

nate function that is available.

A conversion launched on a channel which are not selected on ADCF register will not

have any effect.

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Rainbow-electronics T89C51AC2 Bedienungsanleitung Seite 80