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3. PD1/TxD. FIGnition enables this pin as the USART's TxD pins and transmits video pix-
els through it. It can't be used as a general purpose IO pin unless video is turned off.
4. PD2/INT0. FIGnition's Bootloader uses this as the USB Interrupt pin.
5. PD3/INT1. This pin is used for video SYNC generation.
6. PD4. FIGnition's Bootloader uses this as the USB transmit pin.
7. This is always VCC.
8. This is always GND.
9. This is always a clock input pin. The only way to change this is to reprogram the AVR
fuses using an ICSP.
10. This is always a clock input pin, like pin 9.
11. Port D5. This is free for user I/O.
12. Port D6/AIN0. This is used for audio.It can be used for other purposes to a limited de-
gree (the audio circuitry may interfere with alternative applications).
13. Port D7.This is used as a Row select output for the top row of the keyboard. It can't be
re-used unless the keyboard scanning is disabled.
14. Port B0. Is also used as a Row select output for the bottom row of the keyboard.
15. Port B1. This is used to select the serial Flash chip. It can be re-used to a limited de-
gree if you remove the Flash IC, but the potential dividers may still interfere.
16. Port B2. This is used to select the serial Memory chip. It can't be re-used if you want to
be able to program FIGnition in Forth.
17. Port B3. This is used in SPI mode. It can be used to drive other devices besides the
serial Flash and SRAM using the spi driver in the Forth ROM.
18. Port B4. This is used in SPI mode and can be re-used as for Port B3.
19. Port B5. This is used in SPI mode and can be re-used as for Port B3.
20. AVCC. This is always VCC.
21. AREF. This is unused; you can use this if you want to measure an analog input (the
logger program in the inFUZE bundle uses this pin).
22. GND. This is always GND.
23. PC0. This is used as a column select 0 input. It can't be re-used unless the keyboard
scanning is disabled.
24. PC1. This is used as a column select 1 input. It can't be re-used unless the keyboard
scanning is disabled.
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