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 6800 Address Decoding 
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Joined: Sat Aug 03, 2013 11:02 pm
Posts: 43
Hello. Some May know Me From The 6502 Forum. I am Currently Working On A 6800 Computer, And I Need Help With Address Decoding. I Am Having Trouble Comprehending The Articles And PDFs I Find On Google. I Have Done Research, Im Just Having Trouble. Can Someone Dumb This Topic Down For Me.

Im Using:
Two 6821 PIA
One 64x8 ROM
One 32x8 RAM

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Wed Sep 04, 2013 12:44 pm
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Joined: Tue Dec 11, 2012 8:03 am
Posts: 285
Location: California
I have looked at the 6800 in the past but never used it. I know it is very, very similar to the 6502, and I was just looking back at my address-decoding page in the 6502 primer to see if there would be something to help you, but I guess now I have to ask for more specifics. What parts seem the most mysterious?

I'm wondering about your RAM and ROM sizes too. I assume you mean 64Kx8 (like a 27c512) ROMs and 32Kx8 RAM (like a 62256); but the 6800 has a memory map of 64KB, so you cannot get 160KB of memory, plus I/O in that space, unless you do some sort of banking arrangement with external hardware. A beginner definitely won't be using that much memory anyway.

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Wed Sep 04, 2013 7:07 pm
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Joined: Sat Aug 03, 2013 11:02 pm
Posts: 43
I am reviving that memory problem. I now have decided 16kx4 ROM and 16kx4 RAM. The rest of thememory is for I/O

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Thu Sep 05, 2013 12:47 pm
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Joined: Tue Dec 11, 2012 8:03 am
Posts: 285
Location: California
16Kx4?? Where will you find that? 16Kx8 is a standard size for ROM. To get 16Kx8 RAM, you just use a 32Kx8 (since there's no 16Kx8) and one address pin doesn't get used the normal way.

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Thu Sep 05, 2013 8:02 pm
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