AT32UC3L0256 Atmel Corporation, AT32UC3L0256 Datasheet - Page 536

• Manufacturer Part Number: AT32UC3L0256
• Manufacturer: Atmel Corporation

Specifications of AT32UC3L0256

• Flash (kbytes): 256 Kbytes
• Pin Count: 48
• Max. Operating Frequency: 50 MHz
• Cpu: 32-bit AVR
• # Of Touch Channels: 17
• Hardware Qtouch Acquisition: Yes
• Max I/o Pins: 36
• Ext Interrupts: 36
• Usb Speed: No
• Usb Interface: No
• Spi: 5
• Twi (i2c): 2
• Uart: 4
• Lin: 4
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 12
• Adc Speed (ksps): 460
• Analog Comparators: 8
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 16
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: Yes
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.62 to 3.6
• Operating Voltage (vcc): 1.62 to 3.6
• Fpu: No
• Mpu / Mmu: Yes / No
• Timers: 6
• Output Compare Channels: 18
• Input Capture Channels: 12
• Pwm Channels: 35
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

23.6.3
23.6.3.1
32145A–12/2011
Spread Spectrum Counter
Special considerations
SPREAD field of CR (CR.SPREAD) is zero). When the timebase counter reaches its effective
top value, it restarts counting from zero. The period of the PWMA output waveform is then:
The timebase counter can be reset by writing a one to the Timebase Clear bit in CR (CR.TCLR).
Note that this can cause a glitch to the output PWM waveforms in use.
The spread spectrum counter allows the generation of constantly varying duty cycles on the out-
put PWM waveforms. This is achieved by varying the effective top value of the timebase counter
in a range defined by the spread spectrum counter value.
When CR.SPREAD is not zero, the spread spectrum counter is enabled. Its range is defined by
CR.SPREAD. It starts to count from -CR.SPREAD when the PWMA is enabled or after reset
and counts upwards. When it reaches CR.SPREAD, it restarts to count from -CR.SPREAD
again. The spread spectrum counter will cause the effective top value to vary from TOP-
SPREAD to TOP+SPREAD.
varying duty cycle on the PWM output waveforms though the duty cycle values stored are
unchanged.
Figure 23-2. PWMA Adjusting Top Value for Timebase Counter
The maximum value of the timebase counter is 0xFF. If SPREAD is written to a value that will
cause the ETV to exceed this value, the spread spectrum counter’s range will be limited to pre-
vent the timebase counter to exceed its maximum value.
If SPREAD is written to a value causing (TOP-SPREAD) to be below zero, the spread spectrum
counter’s range will be limited to prevent the timebase counter to count below zero.
In both cases, the SPREAD value read from the Control Register will be the same value as writ-
ten to the SPREAD field.
0x0FFF
0x0
Duty Cycle
SPREAD
TOP
-SPREAD
Figure 23-2 on page 536
T
PWMA
=
ETV
+
Adjusting top value range
for the timerbase counter
1
illustrates this. This leads to a constantly
T
GCLK
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