Rainbow Electronics T89C51CC02 - Manual (Page 114)

114 Rev.A - May 17, 2001
Preliminary
T89C51CC02
17. Analog-to-Digital Converter (ADC)
17.1. Introduction
This section describes the on-chip 10 bit analog-to-digital converter of the T89C51CC02. 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.
17.2. 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
•
VACC Analog supply voltage for ADC
•
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
17.3. 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.