Manual

68
AT90S/LS8535
1041H–11/01
Analog-to-Digital
Converter
Feature list • 10-bit Resolution
• 0.5 LSB Integral Non-linearity
• ±2 LSB Absolute Accuracy
• 65 - 260 µs Conversion Time
• Up to 15 kSPS at Maximum Resolution
• 8 Multiplexed Input Channels
• Rail-to-Rail Input Range
• Free Running or Single Conversion Mode
• Interrupt on ADC Conversion Complete
• Sleep Mode Noise Canceler
The AT90S8535 features a 10-bit successive approximation ADC. The ADC is con-
nected to an 8-channel Analog Multiplexer that allows each pin of Port A to be used as
an input for the ADC. The ADC contains a Sample and Hold Amplifier that ensures that
the input voltage to the ADC is held at a constant level during conversion. A block dia-
gram of the ADC is shown in Figure 45.
The ADC has two separate analog supply voltage pins, AVCC and AGND. AGND must
be connected to GND and the voltage on AV
CC
must not differ more than ±0.3V from
V
CC
. See “ADC Noise Canceling Techniques” on page 74 on how to connect these pins.
An external reference voltage must be applied to the AREF pin. This voltage must be in
the range 2V - AV
CC
.
Figure 45. Analog-to-Digital Converter Block Schematic
ADC CONVERSION
COMPLETE IRQ
8-BIT DATA BUS
15 0
ADC MULTIPLEXER
SELECT (ADMUX)
ADC CTRL & STATUS
REGISTER (ADCSR)
ADC DATA REGISTER
(ADCH/ADCL)
MUX2
ADIE
ADIE
ADFR
ADSC
ADEN
ADIF
ADIF
MUX1
MUX0
ADPS0
ADPS1
ADPS2
8-
CHANNEL
MUX
CONVERSION LOGIC10-BIT DAC
+
-
SAMPLE & HOLD
COMPARATOR
ADC9..0
PRESCALER
AREF
ADC7
ADC6
ADC5
ADC4
ADC3
ADC2
ADC1
ADC0