AT32UC3L-EK Atmel, AT32UC3L-EK Datasheet - Page 604

• Manufacturer Part Number: AT32UC3L-EK
• Description: KIT EVAL AVR32 UC3 MCU
• Manufacturer: Atmel
• Type: MCUr

Specifications of AT32UC3L-EK

• Contents: *
• Silicon Manufacturer: Atmel
• Core Architecture: AVR
• Core Sub-architecture: UC3L
• Kit Contents: Board
• Features: USB / Battery Powered, Board Controller / Bootloader
• Svhc: No SVHC (15-Dec-2010)
• Rohs Compliant: Yes
• Tool Type: Starter Kit
• Cpu Core: AVR 8
• Data Bus Width: 8 bit
• Processor Series: AT32
• Processor To Be Evaluated: AT32UC3L064
• Interface Type: USB, Capacitive Touch
• For Use With/related Products: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

26.6.6
26.6.7
26.6.8
26.6.9
32099F–11/2010
ADC Clock
ADC Sleep Mode
Startup Time
Sample and Hold Time
The Pseudorandom Noise Generator is always enabled when a conversion is in progress, but
the line can be multiplexed with other I/O Controller lines. In this case, the user must make sure
the I/O Controller is configured correctly to allow the noise signal to propagate out to the PRND
pin.
The PRND pin is updated with a new value from the Pseudorandom Noise Generator with inter-
vals given by the following equation:
T
Note that the observed period on the PRND pin will depend on the number of consecutive zeros
or ones that are made by the Pseudorandom Noise Generator.
The ADCIFB generates an internal clock named CLK_ADC that is used by the Analog-to-Digital
Converter cell to perform conversions. The CLK_ADC frequency is selected by writing to the
PRESCAL field in the ADC Configuration Register (ACR). The CLK_ADC range is between
CLK_ADCIFB/2, if PRESCAL is 0, and CLK_ADCIFB/128, if PRESCAL is 63 (0x3F).
A sensible PRESCAL value must be used in order to provide an ADC clock frequency according
to the maximum sampling rate parameter given in the Electrical Characteristics section. Failing
to do so may result in incorrect Analog-to-Digital Converter operation.
The ADC Sleep Mode maximizes power saving by automatically deactivating the Analog-to-Dig-
ital Converter cell when it is not being used for conversions. The ADC Sleep Mode is enabled by
writing a one to the SLEEP bit in the ADC Configuration Register (ACR).
When a trigger occurs while the ADC Sleep Mode is enabled, the Analog-to-Digital Converter
cell is automatically activated. As the analog cell requires a startup time, the logic waits during
this time and then starts the conversion of the enabled channels. When conversions of all
enabled channels are complete, the ADC is deactivated until the next trigger.
The Analog-to-Digital Converter cell has a minimal startup time when the cell is activated. This
startup time is given in the Electrical Characteristics chapter and must be written to the
STARTUP field in the ADC Configuration Register (ACR) to get correct conversion results.
The STARTUP field expects the startup time to be represented as the number of CLK_ADC
cycles between 8 and 1024 and in steps of 8 that is needed to cover the ADC startup time as
specified in the Electrical Characteristics chapter.
The Analog-to-Digital Converter cell is activated at the first conversion after reset and remains
active if ACR.SLEEP is zero. If ACR.SLEEP is one, the Analog-to-Digital Converter cell is auto-
matically deactivated when idle and thus each conversion sequence will have a initial startup
time delay.
A minimal Sample and Hold Time is necessary for the ADCIFB to guarantee the best converted
final value when switching between ADC channels. This time depends on the input impedance
of the analog input, but also on the output impedance of the driver providing the signal to the
analog input, as there is no input buffer amplifier.
PRND
= (PRESCAL[5:3]+1) * 2 * TCLK_ADCIFB
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