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Updated FAQ (markdown)

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tmk 2014-06-19 21:12:04 -07:00
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FAQ.md
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@ -179,3 +179,17 @@ Pressing any key during sleep should wake host.
- http://arduino.cc/en/uploads/Main/arduino-micro-schematic.pdf
Arduino leonardo and micro have **ATMega32U4** and can be used for TMK, though Arduino bootloader may be a problem.
## Using PF4-7 pins of USB AVR(ATMega32U* or AT90USB*)?
You need to set JTD bit of MCUCR yourself to use PF4-7 as GPIO. Those pins are configured to serve JTAG function by default. If you are using Teensy this isn't needed. Teensy is shipped with JTAGEN fuse bit unprogrammed to disable the function.
See this code.
```
// JTAG disable for PORT F. write JTD bit twice within four cycles.
MCUCR |= (1<<JTD);
MCUCR |= (1<<JTD);
```
https://github.com/tmk/tmk_keyboard/blob/master/keyboard/hbkb/matrix.c#L67
And read **26.5.1 MCU Control Register – MCUCR** of ATMega32U4 datasheet.