241
8331B–AVR–03/12
Atmel AVR XMEGA AU
Figure 20-6.
SRAM memory mapping.
20.5
Clock Generation
The USB module requires a minimum 6MHz clock for USB low speed operation, and a minimum
48MHz clock for USB full speed operation. It can be clocked from internal or external clock
sources by using the internal PLL, or directly from the 32MHz internal oscillator when it is tuned
and calibrated to 48MHz. The CPU and peripherals clocks must run at a minimum of 1.5MHz for
low speed operation, and a minimum of 12MHz for full speed operation.
The USB module clock selection is independent of and separate from the main system clock
selection. Selection and setup are done using the main clock control settings. For details, refer
to
”System Clock and Clock Options” on page 83
The
shows an overview of the USB module clock selection.
FIFO
EP_ADDRH_MAX
EP_ADDRL_0
EP_ADDRH_0
(MAXEP+1) x 4 Bytes
Active when FIFOEN==1
ENDPOINT
DESCRIPTORS
TABLE
STATUS
CTRL
CNTL
CNTH
DATAPTRL
DATAPTRH
AUXDATAL
AUXDATAH
ENDPOINT
0 OUT
STATUS
CTRL
CNTL
CNTH
DATAPTRL
DATAPTRH
AUXDATAL
AUXDATAH
ENDPOINT
0 IN
STATUS
CTRL
CNTL
CNTH
DATAPTRL
DATAPTRH
AUXDATAL
AUXDATAH
ENDPOINT
MAXEP IN
(MAXEP+1) x 16 Bytes
FRAME
NUMBER
FRAMENUML
FRAMENUMH
2 Bytes
Active when
STFRNUM==1
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
(MAXEP+1)<<4
EPPTR
EPPTR +
(MAXEP+1)*16
SRAM
ADDRESS