Rainbow Electronics T89C51AC2 - Manual (Page 80)

80
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.)
• 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
• 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.