Atmel STK526, Руководство пользователя, Страница: 12 / 38

Using the STK526
2-12 STK526 rev. B Hardware User Guide
7709B–AVR–05/07
2.3.3 STK500 RESET
(c.f.
“RESET from STK500” on page 19
)
2.4 AT90USB82/162 AVR Microcontroller
2.4.1 Main Clock XTAL
To use the USB interface of the AT90USBxxx, the clock source should always be a
crystal or external clock oscillator (the internal 8MHz RC oscillator cannot be used
successfully to operate with the USB interface). Only the following crystal frequency
allows proper USB operations: 8MHz, 16MHz. The STK526 comes with a default 8MHz
crystal oscillator.
When closing STKX1 and STKX2 switches, and STK526 is connected to an STK500,
the STK526 can operate with the “STK500 Osc” frequency parameter. The STK500
clock precedes the crystal connected.
2.4.2 Analog Power Supply
AVCC AVCC is tied to VCC by hardware.
2.5 Serial Links
2.5.1 USB
The STK526 is supplied with a standard USB type-B receptacle (identifying the board as
a Device only) that aim to receive a B-plug
Figure 2-8 . USB type-B receptacle
VBUS Detection The board also implement a VBUS detection on a generic I/O. A low-power (50µA)
voltage divider (/2) is connected from VBUS to PortC bit 2 pin. The VBUS presence is
detected with a high level on the MCU pin.