AT90USB647-MU Atmel, AT90USB647-MU Datasheet - Page 40

• Manufacturer Part Number: AT90USB647-MU
• Description: MCU, 8BIT, 64K FLASH, USB, 64QFN
• Manufacturer: Atmel

Specifications of AT90USB647-MU

• Controller Family/series: AT90
• No. Of I/o's: 48
• Eeprom Memory Size: 2KB
• Ram Memory Size: 4KB
• Cpu Speed: 16MHz
• No. Of: RoHS Compliant
• Core Size: 8bit
• Program Memory Size: 64KB
• Oscillator Type: External, Internal
• Package: 64QFN EP
• Device Core: AVR
• Family Name: AT90
• Maximum Speed: 20 MHz
• Ram Size: 4 KB
• Operating Supply Voltage: 3.3|5 V
• Data Bus Width: 8 Bit
• Program Memory Type: Flash
• Number Of Programmable I/os: 48
• Interface Type: SPI/TWI/USART/USB
• On-chip Adc: 8-chx10-bit
• Operating Temperature: -40 to 85 °C
• Number Of Timers: 4
• Lead Free Status / Rohs Status: Details

6.1.4
6.1.5
6.1.6
6.2
6.2.1
6.2.2
40
Clock Sources
AT90USB64/128
Asynchronous Timer Clock – clk
ADC Clock – clk
USB Clock – clk
Default Clock Source
Clock Startup Sequence
The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked directly
from an external clock or an external 32 kHz clock crystal. The dedicated clock domain allows
using this Timer/Counter as a real-time counter even when the device is in sleep mode.
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O clocks
in order to reduce noise generated by digital circuitry. This gives more accurate ADC conversion
results.
The USB is provided with a dedicated clock domain. This clock is generated with an on-chip PLL
running at 48MHz. The PLL always multiply its input frequency by 24. Thus the PLL clock regis-
ter should be programmed by software to generate a 2MHz clock on the PLL input.
The device has the following clock source options, selectable by Flash Fuse bits as shown
below. The clock from the selected source is input to the AVR clock generator, and routed to the
appropriate modules.
Table 6-1.
Note:
The device is shipped with Low Power Crystal Oscillator (8.0MHz-max) enabled and with the
fuse CKDIV8 programmed, resulting in 1.0MHz system clock (with a 8 MHz cristal). The default
fuse configuration is CKSEL = "1110", SUT = "01", CKDIV8 = "0". This default setting ensures
that all users can make their desired clock source setting using any available programming
interface.
Any clock source needs a sufficient V
cycles before it can be considered stable.
To ensure sufficient V
the device reset is released by all other reset sources.
describes the start conditions for the internal reset. The delay (t
Oscillator and the number of cycles in the delay is set by the SUTx and CKSELx fuse bits. The
USB
ADC
Device Clocking Option
Low Power Crystal Oscillator
Reserved
Low Frequency Crystal Oscillator
Reserved
Calibrated Internal RC Oscillator
External Clock
Reserved
1. For all fuses “1” means unprogrammed while “0” means programmed.
Device Clocking Options Select
ASY
CC
, the device issues an internal reset with a time-out delay (t
CC
to start oscillating and a minimum number of oscillating
(1)
“On-chip Debug System” on page 56
TOUT
) is timed from the Watchdog
1111 - 1000
0111 - 0110
0101 - 0100
CKSEL3..0
0011
0010
0000
0001
7593K–AVR–11/09
TOUT
) after