9- dealing with analog signals by sherif.abas


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									                 Analog Comparator

• Positive input chooses bet. PB2 and Bandgap Reference.
• Negative input chooses bet. PB3 and the 8 inputs of the A/D.
• ACME= Analog Comparator Mux Enable (Bit 3 in Special
Function I/O Reg.)
Analog Comparator Control and Status Reg.:
           Analog-to-Digital Converter

• 10-bit successive approximation
• 0.5 LSB Integral Non-linearity
• ± 2 LSB Absolute Accuracy
• 65 - 260 μs Conversion Time
• Up to 15 kSPS at Maximum Resolution
• 8 Multiplexed Single Ended Input Channels (PA0 -> PA7)
• 7 Differential Input Channels (between any input and
• Optional Left Adjustment for ADC Result Readout
• 0 - VCC ADC Input Voltage Range
• Separate supply voltage pin, AVCC Pin 30 (should be VCC
±0.3 V)
• Selectable 2.56V internal Reference Voltage, AVCC, or
external reference (Pin 32)
• Free Running or Single Conversion Mode
• Interrupt on ADC Conversion Complete
• Sleep Mode Noise Canceller
• Auto Triggering is enabled by setting the ADC Auto Trigger
    Enable bit. This provides a method of starting conversions at
    fixed intervals. Using the ADC Interrupt Flag as a trigger
    source makes the ADC start a new conversion as soon as the
    ongoing conversion has finished. The ADC then operates in
    Free Running mode.
• The channel and reference selection is continuously updated
    until a conversion is started. In Free Running mode, always
    select the channel before starting the first conversion or wait
    for the first conversion to complete, and then change the
    channel selection. Since the next conversion has already
    started automatically, the next result will reflect the previous
    channel selection. Subsequent conversions will reflect the
    new channel selection.

• ADC Noise Canceler (ADC Noise Reduction mode/ Idle mode)
  enables conversion during sleep mode to reduce noise
  induced from the CPU core and other I/O peripherals.

• Output = Vin .1024 / VREF
• Single ended channels:

Registers associated with A/D:

   ADC Multiplexer SelectionRegister

   ADLAR Bit 5 = 0 : right adjust the result
                 = 1 : Left adjust the result
   If the result is left adjusted and if no more than 8-bit precision
   is required, it is sufficient to read ADCH

                                        A/D DATA REGISTERS

   • MUX 3-4 are used by differential  input signals (The differential
    input channels are not tested for devices in PDIP Package). In
    this case different values of Gain can be selected (1,10,200)
ADC Control and Status Register A

 • ADEN Bit 7=1: A/D Enable; =0: turn A/D off even during
 • ADSC Bit 6=1: A/D Start Conversion
 • ADATE Bit 5=1: Auto Triggering of the ADC is enabled. The
   ADC will start a conversion on a positive edge of the selected
   trigger signal. The trigger source is selected by setting the
   ADC Trigger Select bits, ADTS in SFIOR
 • ADIF Bit 4: A/D Interrupt Flag is set when an A/D conversion
   completes. By disabled int this bit is cleared by writing a ‘1’.
 • ADIE Bit 3=1: A/D Interrupt Enable
 • Prescalaing:
          APDS2-APDS0                 Prescalar
                0-7                   2-2-4-8-16-32-64-128
(the successive approximation circuitry requires a clock frequency
between 50 kHz and 200 kHz to get maximum resolution)
Special Function I/O Register:

 ADTS2-0: ADC Auto Trigger Source Selections:

                                           (ADC INT flag)

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