I mentioned on Chad’s (sburrow) newbie thread that we more experienced designers should help newbies with a 6502-based EPROM programmer that is cheap, easy to build, and contain no programmable components (not even boot strap EPROM). It is a good way to provide newbie with an EPROM programmer and teach about 6502 hardware/software and components can be reused for other projects. Please provide a link if that already been done and is public domain design. If not, let this be a challenge!
Bill

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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?

(Thanks for the new thread!)

I ask this not to sound snarky, but just curious...

Why would anyone out there consider a ROM these days, especially in a 6502 project?
I have done many 6502 systems now, and have never used or will ever us a ROM.

When I first started, I looked at using a ROM and then ran into the same that most do; expensive programmer, slow access time, fiddly to reprogram in a hurry.

So instead, I used a $1.50 AVR and its inexpensive programmer. I have also used PICs, although the AVR32 series cost the same and are fast enough to actually emulate a ROM in a 6502 system directly.

How I do it is by connecting the AVR in parallel to the SRAM running the 6502. Right away, you now have many options for RAM in sizes from 2K to 512K with speeds as good as 10ns and in DIP packages. At 10ns, you can get a 65C02 smokin' along at over 10MHz with ease.

To "Boot", the AVR simply pulls on the BE / RS line of the 65C02, and then dumps it's contents to the SRAM. After that, it tristates all pins and goes to sleep, allowing the 6502 to run fully from the fast SRAM and allow read/write to the entire 64K of space.

To program my code, I use one of the PC based assemblers (Kowalski is my fav), and then include the binary in the AVR program to be uploaded. Now I can code on the PC, and with a few clicks, see the 6502 running my code. This is also all done in circuit - no pulling a ROM for programming.

SO for a fraction of the cost of the ROM method, you get a MUCH faster system, way more memory options, and instant code and load.

And if all of that isn't reason enough to call now and order your ROMless system, get a lod of this...

Any of the 20MHz AVR's are fast enough to directly emulate ROM in a 1MHz 6502 system. So you can bypass the SRAM altogether and connect one AVR to the 6502. Plug in your Atmel-ICE, and you can program your 6502 system in less steps than a friggin Arduino! Code and load!

So I must ask... why bother with ROM at all, unless doing an OEM rebuild on some vintage gear?

Here is one of my many ROMless projects, this one running directly from the AVR. The programmer shown here allows me to code 6502 assembly on the PC, press one button and then see the code running on the 6502. The other ICs on the board support the AVR further, allowing VGA generation, so this is a complete 6502 SBC that can put out color video with only 4 ICs.



Brad

You know, that might be a good question for a different thread...

Or if you consider an AVR programmer and its target to be a legitimate ROM as I do, it would fit right into this thread!
Actually, once programmed, the AVR is indeed a ROM, and to build it, one just needs to bend a 6 pin header to fit a breadboard.

A 100mmx100mm pc board in a manila envelope weights under 2oz and can be shipped anywhere in USA for 70 cents or Canada for $1.30, or $2.60 to rest of the world. I know, because I’ve done it many times without any problems. JLCPCB built 10 boards for $5 so I have plenty spare PC boards to give away, so it is basically free material and trivial shipping cost. An EPROM is quite a bit more expensive and a pc board is still needed.



I’m with you regarding ROM-less designs, vast majority of my own designs are ROM-less with the help of programmable CPLD; they are smaller and faster but they are more complicated and distract from the study of 6502. Newbies want to see a classical microprocessor design. The proposed EPROM programmer is in fact ROM-less, surely we have the expertises to design a ROM-less (or Arduino-less, or CPLD-less) 6502 SBC?

_________________
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?

The "classical" aspect makes sense. This hobby is often a journey to the past more than anything.

I wonder how many 6502 "newbs" started like me, having plenty of 8 Bit "modern" micro-controller experience (Arduino included), but wanted to take a roll down memory lane? When I initially seen all of the 6502 projects, I was turned off by the ROM / ROM Programmer requirement. Even some of the 65C02 SBC's were ending up reliant on an ebay dinosaur to program horrendously slow (150ns) ROMS.

A modern solution using modern components would be great. The $1.50 microcontroller was the only answer I came up with, so I am throwing it into the ring, since most newbs probably have this hardware on their bench.

The other win is to have in-circuit programming. Learning 6502 assembly, I make more revisions per hour than I take breaths. Imagine having to pull a ROM each time!! Forget it! A modern solution for newbs MUST have in circuit programmability and allow assembling / loading from a PC.

Brad

I haven't attempted to use an EPROM, but I was using EEPROMs for a bit and it was pretty much trivial to program it with an Arduino. No eBay dinosaurs required.
It felt a bit silly to put a microcontroller in my system that's more powerful than the overall computer, which is why I didn't try a microcontroller to store programs.

I can agree, and when I am trying to keep to era specific parts it does feel "dirty" to toss any kind of modern uC in the mix.

On a humorous note, all this talk got me looking on digikey for the going rate on 32k EEPROM. Perhaps I should buy a few of these?...

https://www.digikey.ca/en/products/detail/microchip-technology/AT28C010-12DM-883/523530

That's only five bucks per kilobyte! How do they make it so cheap??
Doh!

_________________
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?

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

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

FWIW, I’m a newbie and I preload RAM with a microcontroller (Raspberry Pi Pico) with a simple circuit that latches the data and address lines, holds CPU in high Z, then resets the CPU when ready. Takes roughly quarter of a second to populate the RAM.

Once I make code changes, I can upload to the device and have it completely running in about 10 seconds. I don’t have any EPROMs or a burner and no real urge to get any.

Total cost under $10, including all components and the Pico. Maybe I’m not your average newbie, I dunno.