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@@ -184,22 +184,15 @@ Pressing any key during sleep should wake host.
184 184
185Arduino Leonardo and micro have **ATMega32U4** and can be used for TMK, though Arduino bootloader may be a problem. 185Arduino Leonardo and micro have **ATMega32U4** and can be used for TMK, though Arduino bootloader may be a problem.
186 186
187## Enabling JTAG
187 188
188## Using PF4-7 Pins of USB AVR? 189By default, the JTAG debugging interface is disabled as soon as the keyboard starts up. JTAG-capable MCUs come from the factory with the `JTAGEN` fuse set, and it takes over certain pins of the MCU that the board may be using for the switch matrix, LEDs, etc.
189You need to set JTD bit of MCUCR yourself to use PF4-7 as GPIO. Those pins are configured to serve JTAG function by default. MCUs like ATMega*U* or AT90USB* are affected with this.
190 190
191If you are using Teensy this isn't needed. Teensy is shipped with JTAGEN fuse bit unprogrammed to disable the function. 191If you would like to keep JTAG enabled, just add the following to your `config.h`:
192 192
193See this code. 193```c
194#define NO_JTAG_DISABLE
194``` 195```
195 // JTAG disable for PORT F. write JTD bit twice within four cycles.
196 MCUCR |= (1<<JTD);
197 MCUCR |= (1<<JTD);
198```
199https://github.com/tmk/tmk_keyboard/blob/master/keyboard/hbkb/matrix.c#L67
200
201And read **26.5.1 MCU Control Register – MCUCR** of ATMega32U4 datasheet.
202
203 196
204## Adding LED Indicators of Lock Keys 197## Adding LED Indicators of Lock Keys
205You need your own LED indicators for CapsLock, ScrollLock and NumLock? See this post. 198You need your own LED indicators for CapsLock, ScrollLock and NumLock? See this post.