Commodore 64 I/O ROM Expansion Port


Posted on Feb 5, 2014

The output F1 pin 17 of the PLA U17 goes `low` when the BASIC ROM is selected. The KERNAL ROM resides at locations $E000 - $FFFF. The output F2 pin 16 of the PLA U17 goes `low` when the KERNAL ROM is selected. The CHARACTER GENERATOR ROM resides at locations $D000 - $DFFF. The output F3 pin 15 of the P


Commodore 64 I/O ROM Expansion Port
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LA U17 goes "low" when the Character Generator ROM is selected. The expansion port is an extension of the microprocessor address, data, and control bus. ROML decodes addresses $8000 - $9FFF, and ROMH decodes addresses $E000 - $FFFF. These are outputs from the PLA used to select the catridge inserted in the expansion port. I/O 1 input from U15 decodes addresses $DE00 - $DEFF. I/O 2 output from U15 decodes addresses $DF00 - $DFFF.




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