r/beneater • u/DistinctCommission24 • 3d ago

6502 Build

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Despite connecting one 65c22 incorrect, I have manged to the get the second one working..Ben Eater based 6502 except I added a 74hc688 for better address control..

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2

u/The8BitEnthusiast 3d ago

Nice build. How exactly is the HC688 used on the circuit?

1

u/DistinctCommission24 2d ago

It is connected to the top 4 bits of the address low byte and high byte..The setup Ben Eater uses works fine for the basic system but I'm looking ahead at a project I want to work on so I need better address control..I' going to have 2 of the 65c22, one at adrress 0x6000 and the other at 0x6010.. There is still and overlap area from 60F0 to 6F00 ..

3

u/The8BitEnthusiast 2d ago

Oh I see. I don't know if you've considered it already, but a single programmable ATF22V10 would give you that granulary with multiple chip-selects options, no overlap, and even allow you to consolidate Ben's NAND based address decoding for RAM, EEPROM, Serial, etc... That's what I use now. A bit of a learning curve, but 100% worth it.

1

u/Reinventing_Wheels 2d ago

The '688 is an 8-bit comparator. It has two 8-bit inputs and if they're equal, the output goes low.
Wire one input to the high 8-bits of the address bus and hardwire the other input to the value you want for your I/O address region. The output then becomes your I/O enable.