Now that I have tested my 6502 and having a basic knowledge of what's going on, I want to start adding some memory. I would like start with a ROM(EEPROM) for now coz' I don't have any RAM yet. I have a Winbond W27c512 EEPROM that i would like to start with. So the address pins of the W27c512 (A0..A15) goes to the address bus pins of the 6502 and the same with the data pins, correct? What about the OE and CE? I'm guesing they should held low? If so, why?



So while I experiment with just a ROM I would like to know any recommended RAM I should buy? 16k or 32k I guess.

The 6502 datasheet says it can address a total of 65k of memory which I don't understand quite well yet. When it says 65k memory, does it mean 65k for just ROM and I can add say a 16k or 32K RAM too? Or a total for both like for example 32k ROM + 32k RAM? Or 32k ROM + 16k RAM + other inputs = 65k?

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// tinkerBOY

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Thank you!

What about just the ROM for now? The one i have is 64k(w27c512) with address pins A0 to A15. So is it a straight connections to the 6502 including the A15? Do i still need some decoding if im just going to use just a ROM?

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// tinkerBOY

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Yes I know that. But since I don’t have any RAM or I/O parts i might as well learn with just ROM for now.

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// tinkerBOY

So any parts recommended for a RAM or even an EEPROM?

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// tinkerBOY

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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

My RC6502 Apple 1 Replica uses an Amtel AT28C256 for ROM and Hitachi HM62256BLP-7 for RAM, and works nicely. These are both pretty common parts used throughout the hobbiest community, with many non-official sources as well (although you need to be alert for used, possibly not tested, and possibly remarked chips from China, I suppose).


These can be had for closer to a tenth that price (often even with free shipping) from many vendors on AliExpress. With the usual "buyer-beware" warnings, of course.

On Ebay and the like there are also plenty of sellers of packages of various chips that include RAM and ROM; much of the RAM and ROM in my parts bin has come from those. (For example, I saw a good deal on a 68008 that I wanted to try out, and the seller had packaged it with enough other stuff for a full computer, sans decoding logic.) The RAM chips I currently have in my parts bin (mostly untested so far), include:


(The chips just seem to collect, like socks in a laundry room! :-))

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Curt J. Sampson - github.com/0cjs

I bought a couple of Amtel AT28C256 for ROM and Hitachi HM62256BLP-7 just a while ago. I hope it arrives sooner as I'm excited to tinker and decide what 6502 build im gonna be doing.

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// tinkerBOY

For a RAM, this part will work.

Realistically, any computer without RAM and I/O is all but useless. In the case of the 65C02, there are two "must have" areas of RAM if any reasonable program is to be executed: page zero and page one. Many instructions have zero page addressing modes and some instructions are 100 percent dependent on page zero access to work, e.g., LDA (<addr>),Y.

Page one is important because the 65C02's stack is "hard-wired" to that range of addresses. The stack pointer is an eight-bit register, which means you cannot point at any address outside the range $0100-$01FF.

As for ROM, a 32KB EPROM (27C256) or EEPROM (28C256) is way more that enough. You can cram a lot of code and/or data into a ROM that size. In reality, you probably will use a fraction of that space and could get by with something smaller.

Unfortunately, sources for parallel interface E(E)PROMs are dwindling and prices are increasing. My long-time go-to EPROM was the 27C256-55, which has vanished from first tier distribution. One second tier distributor quoted me 13 dollars each on them—I bought quite a few from Jameco a few years ago for about four dollars each.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!