circuit.txt

利用AVR单片机实现的慢速USB设备协议

Some comments about the hardware:

(1) If you use this circuit to switch mains voltage, be CAREFUL! If the high
voltage section is not properly shielded and insulated, you may damage the
circuit, the computer connected to it or you may even endanger your life!

(2) Switching inductive loads may cause electromagnetic interference (EMI).
To protect the circuit from EMI, you may need the usual shielding and
filtering.

(3) The circuit does not include brownout detection. When the voltage drops
slowly (which can happen with the 1000uF filter capacitor in the power
supply), the CPU may execute random instructions and thus modify the EEPROM.
You will notice that the EEPROM has been modified if the status of the
switches is not preserved across power-down. In this case please add your
favorite brownout protection. See e.g. Atmel's Application Note AN180. The
ATtiny2313 device includes brownout detection on chip.

(4) We recommend that you use the ATtiny2313 which is specified for the
high clock rate. The AT90S2313-10 may cause considerable trouble with EMI.
Remember that it runs at almost twice the specified speed! [You may consider
running the AT90S2313-10 at 5V, but then the USB signals are outside the
specified voltage range. However, implementations are required to survive
this voltage.]

(5) The CPU is supplied by both, the USB bus and a separate power supply.
The USB supply ensures that the CPU is not damaged when connected without
supply. It is not intended for operation. The separate supply ensures that
the device works without a host.