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6809 instead of the 6502


EvilSnack
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On 10/27/2021 at 6:06 PM, Wavicle said:

I was going to say because they don't make them anymore, but apparently that isn't true. That said, new stock is expensive and limited to 2MHz.

True, though X16 isn't letting the whole "no new stock" thing stand in the way of sound chips, so hacking an old 6809 or similar chip is doable from that perspective.

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It was always such a shame that the 6809 got paired so much with the 6847 which makes games look like the colour was vomited onto the screen (I presume there was some technical reason for those colours because no sane person would choose them voluntarilY).

An 8Mhz 6809 (in FPGA) and Vera would be an awesome machine.

Also it's enjoyable writing for that sort of CPU. Writing 6502 assembler you always feel you are fighting it.

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On 10/27/2021 at 3:03 PM, EvilSnack said:

Aside from having to rewrite the entire ROM, and perhaps having to add an adapter to accommodate any pin-out/power requirement variation between the two CPUs, what's stopping an ambitious experimenter from replacing the 6502 with a 6809?

Though it wouldn't be necessary to replace the 6502 it it's on a bus mastering expansion card.

Edited by BruceMcF
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What actually speaks for a 6502 (or sibling) except of the nostalgia factor and to reuse some parts of existing C64 software? Aren't there better 8 bit processors? Because of the different hardware, especially VERA, software needs to be adopted anyway.

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With better I mean for example:

1) does it need additional chips for timers, ports?
2) are other processors with more registers faster/slower for the same tasks?
3) what is the available max. clock count (related to 2)?

Independent of that - how large is the effort to adopt software to run on the X16, especially compared with other 8-bit processors? IIRC, the 6502 was not part of the "dream 8-bit computer definition".

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On 10/29/2021 at 9:34 AM, Ju+Te said:

With better I mean for example:

1) does it need additional chips for timers, ports?
2) are other processors with more registers faster/slower for the same tasks?
3) what is the available max. clock count (related to 2)?

Independent of that - how large is the effort to adopt software to run on the X16, especially compared with other 8-bit processors? IIRC, the 6502 was not part of the "dream 8-bit computer definition".

There are microcontrollers built around a 6502 style core, so sometimes you don't need extra chips.

Faster and slower varies based on usage. 6502 had a slower clock usually than 8088, but the 6502 was more efficient at memory access so clock speed didn't matter in those types of cases. But with more registers it might not be as big of a deal. So faster clock isn't always better.

6502 was definitely part of David's "manifesto" as he wanted an 8bit computer like unto the C64 or VIC-20. And we can have much faster 6502 style computers today than were practical back then.

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On 10/29/2021 at 8:34 AM, Ju+Te said:

With better I mean for example:

1) does it need additional chips for timers, ports?
2) are other processors with more registers faster/slower for the same tasks?
3) what is the available max. clock count (related to 2)?

Independent of that - how large is the effort to adopt software to run on the X16, especially compared with other 8-bit processors? IIRC, the 6502 was not part of the "dream 8-bit computer definition".

I found out about the project after the first "Building my dream computer" video, so I am not certain about things prior to that, but in that video 6502 was definitely part of the plan. The original plan was to use a C64 with the video, keyboard, and storage hanging off expansion ports. This would give a stable platform for developing the kernal and once done the C64 PCB should be replaceable by any commodity (or bespoke) 6502 PCB.

I've worked on teams building hardware or silicon ASIC products for the last 15 years and thought this original plan was well grounded: it kept things simple; started from a known working point; and provided a fast path for the software team to start developing on real hardware. Somewhere along the way, feature creep came to visit and promptly made starting with a C64 impossible. My experience told me that this was going to result in higher cost, longer dev time, or both -- but that experience is limited to commercial efforts at companies with deep pockets so maybe it wasn't tuned for this environment... or maybe it was. Switching to an MC6800 variant would be committing to this all over again unless there is a readily available source of commodity MC6800 boards.

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On 10/30/2021 at 2:16 AM, Ju+Te said:

The emphasis laid on "it would have a real CPU" (probably in contrast to some emulation or FPGA) and the 6502 only was mentioned in the accessory sentence. So it seems, both views are valid.

dream-computer-requirements.png

True. There was some evolution of the ideas over time, from his initial blog post to that video and subsequent videos.

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  • 4 weeks later...

I understand the reasons why few would attempt this. The 6809 seems to have been a victim of bad timing. I've coded for both the 6502 (including a word processor for my C64) and the 6809 (several attempted games for Dad's CoCo), and the latter simply had that much more potential.

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On 11/26/2021 at 2:18 PM, EvilSnack said:

I understand the reasons why few would attempt this. The 6809 seems to have been a victim of bad timing. I've coded for both the 6502 (including a word processor for my C64) and the 6809 (several attempted games for Dad's CoCo), and the latter simply had that much more potential.

As many companies have proven over time, you don't have to have the best product to gain the most traction and take control of the marketplace.

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On 11/26/2021 at 3:15 PM, Scott Robison said:

As many companies have proven over time, you don't have to have the best product to gain the most traction and take control of the marketplace.

Yes - I think pricing may be a factor, according to the wikipedia article - https://en.wikipedia.org/wiki/Motorola_6809

I had the pleasure of using a SuperPet in  the 80's and all the Waterloo languages - they had dual CPUs of a 6502 and the 6809.

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On 11/26/2021 at 8:05 PM, Edmond D said:

Yes - I think pricing may be a factor, according to the wikipedia article - https://en.wikipedia.org/wiki/Motorola_6809

I had the pleasure of using a SuperPet in  the 80's and all the Waterloo languages - they had dual CPUs of a 6502 and the 6809.

I've heard a lot of good about 6809. My wife's uncle swears it is the best CPU ever. 🙂

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Alas, as a teenager at the time CPU type was a small thing compared to the amount & quality of accessible software (read games😀) the platform had. The only 6809 specific software I had access  to was the Waterloo languages. They were great for learning and set me up for the many other languages that followed. 

I'm not sure if the X16 had a 6809 I'd be so eager to buy one (or others) given the amount & volume of 6502 based computer systems (and games) from the 80's. That's not to say the 6809 systems were bad; the  just weren't what I used.

Going back to the originating post, once the X16 ships then perhaps someone will experiment with such as system. Perhaps  when/if a stand alone VERA board is released, a 6809 system is designed to use it.

 

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On 11/27/2021 at 12:42 PM, Edmond D said:

Alas, as a teenager at the time CPU type was a small thing compared to the amount & quality of accessible software (read games😀) the platform had.

The functional equivalent of "how many games does it have"?, for this project, would be the supply of skilled assembly language programmers for the processor in question who are willing to donate time to writing the low level Kernel code. Not just the "main guy", but suppose the "main guy" drops out, what are the chances of finding a replacement?

There would be a lot more project risk pursuing a project like this based in a CPU family other than 6502 or z80 families.

However, once the X16 is released, then -- at least as the expansion card interface has been described so far -- it should be possible to do a "Super PET" approach and make a bus mastering 6809 card, for people who want to pursue that.

 

 

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On 11/27/2021 at 3:41 AM, kelli217 said:

It's certainly in the running for the best 8-bit CPU ever. I don't think an OS like OS-9 could have been written on anything else.

I'd have to interject with the Hitachi 6309, but that's essentially a 6809 clone with additional registers including a 32-bit and 2 16-bit accumulators for 32 and 16-bit math as well as hardware divide, block moves, and bit manipulation instructions.

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