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===== DigiCDC - Digispark USB CDC Serial Library =====

The DigiCDC library allows the Digispark or Digispark Pro to appear to a computer as a Virtual Serial Port when connected by USB. This makes it appear just like a standard Arduino and allows the use of the Serial Monitor built into the Arduino IDE.

The DigiCDC library is based on V-USB - because the Digispark does not have hardware USB support. This presents some unique limitations in how it works - outlined below:

  - You must explicitly include the DigiCDC library - by placing the following at the top of your sketch <code>#include <DigiCDC.h></code>
  - It uses a lot of RAM - half of the Digispark's RAM - so only include it when needed and watch your RAM usage. You can wrap strings in F() (ie. SerialUSB.print(F("test")) ) to put the string in flash memory instead of RAM
  - You use it the same as Serial on an Arduino but with SerialUSB instead (ie. SerialUSB.read() instead of Serial.read() ) - The Pro also has Serial defined - but that refers to the hardware Serial port on Pins 6 and 7.
  - The begin statement does not need a baudrate - it is a CDC device so it does not have a set baud rate - just use SerialUSB.begin()
  - You must install the driver for windows - it is part of the driver package found in the Digispark Arduino release. 
  - It is slow - it transfers data very slowly - because it is a low speed USB device doing the job of a Standard speed device - and doing it all virtually without actual hardware support!
  - Like all of our V-USB libraries you must use its delay function instead of delay() - so use SerialUSB.delay() when you need a delay in your code.
  - SerialUSB.delay() or SerialUSB.refresh() must be called every 10ms or less in your code if no other SerialUSB call is made in that code.
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