Hi all,
Apologies for the delay in getting back to this post,
So many responses where to start,
I'll start with Chads reply,
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- No new-old stock chips, everything must be easily obtained from Mouser or Digikey in mass quantity.
If one wants to make the lowest cost project / kit, whether for sale or personal use, then old parts are probably the way to go....with some risk of receiving dud parts. New, WDC, parts from Mouser are not cheap. One will require new parts to run at higher speeds.
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- Chip flexibility as much as possible, especially with RAM and ROM chips. Multiple types/sizes can be plugged into the same socket and will function exactly the same.
I managed to get away with "strandard" parts like the 6264 (8kbyte) / 62256 (32kbye) (55ns) and Microchip SST39SF010/020/040. I saw no point in allowing for things like 27Cxxx EPROM's and am not a fan of the 28 series EEPROM's. I did not see this as a requirement.
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No CPLD's and FPGA's, mainly because I cannot find a good way to program current ones from Linux (as I refuse to use Windows long-term).
I find the whole Windows vs Linux thing interesting, but that a topic for another day. I'm a Windows user....
I think CPLD's, specifically the (MAX7000)EPM7128 / Microchip AT1508, are the way to go.
Forget Wincupl, Use the Altera (Intel) tools and draw schematics and simulate. I can't program HDL/VHDL....on my leaning list.
The CPLD above is actually quite limited. Just enough for basic VGA, complex address decoding with latches for high address etc.
Much more efficient than breadboarding and fewer mistakes in PCB layout. EPM7128 is obsolete, but low cost and still available. Microchip AT1508 is more expensive and still in production. If anybody wants to know more just ask.
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- I/O devices must also be easy to obtain. I have picked PS/2 Keyboards and VGA monitors which are both easy to interface and easy to obtain from Amazon, Walmart, and Newegg.
PS2 keyboards are becoming hard to buy in stores in Australia.
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- Must be useful and can play games, so using *only* a 16x2 LCD would not be enough in the whole scheme of things.
- Must be self-reliant, no need to use with a modern PC, serial connections, or bootstrapping, everything needed is on the ROM. Having serial connection or other means of communicating would be merely a bonus.
Agree, need to have video either VGA, TMS9918 or similar.
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- Power supply comes from USB wall charger, which everyone and their grandma has to charge their phones.
Your logic is sound as everyone has 20 of these lying around their house, but personally I'm not a fan. Other replies have made valid comments on this.
Personally I would prefer to regulate down to the required voltage on a PCB rather than feed it in from an external source.
My design will end up requiring around 18V as I want 15V to be able to power some A-to-D/D-to-A parts (on plugin cards) and audio amplifier requires 10-22V.
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- Solder-it-yourself with helpful user guide which also instructs on how both the hardware and software work. Educational in nature. I think the guide for the Dodo is an excellent model of user-friendliness mixed with education!
I was not planning solder it your self as I have used SMT for the resistors / capacitors and power supply.
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- Total cost under $100, but I think I managed to get mine to $75 comfortably by not using a 6522 VIA on the main-board.
The price of a board is tricky. Has anybody calculated the cost of WDC parts? (Let's use Mouser 1 piece price)
W65C22N6TPG-14 USD10.5
W65C02S6TPG-14 USD10.75
AS6C6264-55PCN USD4.03 (8kbyte)
AS6C62256-55PCN USD4.10 (32kbyte)
AS6C4008-55PCN USD6.38 (512kbyte)
SST39SF010A-70-4C-PHE USD2.92 (128kbyte)
SST39SF040-70-4C-PHE USD3.91 (512kbyte)
Depending on your design you are already at USD30.
In my design I have 1 x 62256, 3 x 6264, 2 x SST39SF040A and 1 x AS6C4008-55PCN, but I could drop one SST39SF040A and the AS6C4008-55PCN leaving it to the buyer to buy later.
I thought of having the PCB assembled in China (I already have several projects in production in China.) and shipping it without the major IC's.
I would fit tested CPLD's and AY-3-8910. Why ship WDC part from USA to Australia and back again. Make it an option, with or without major parts.
All parts socketed of course.
(Another topic we could spend hours on is how do the Chinese make certain things so cheap. I often see items on Ebay / Aliexpress where the parts from Mouser cost more than the item.)
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And you? Could I ask you the same question Andre?
I guess like many of you here I wanted to build my own. That was part of the challenge. I've never bought kits even when it came to 8051, AVR, ARM etc. I would just study the datasheet and make a PCB.
As an electronics engineer getting started was easier. If I were a programmer or someone with no real hardware/software background then I would probably have started with a kit and progressed from there.
The choice of kit would come down to what I could afford.
I would probably buy an assembled SBC if I had no assembly equipment / skills.
I would want some type of screen (VGA/TMS9918 etc.) and keyboard otherwise your programing options are limited.
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cbmeeks wrote:
Hope this isn't too OT but someone mentioned that kits aren't the target audience for the people on this forum...I think there is really a nice market for a "ready-made" 6502 computer that is cheap and somewhat powerful.
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BigDumbDinosaur wrote:
That has been something that has come up around here again and again. As always, the idea ultimately collapses from “design-by-committee” disease. I know that the idea goes back some 20 years and other than Daryl’s SBC series, has not come to fruition.
I like these thoughts but agree that there are problems when it comes to “design-by-committee”.
Not having a common platform is something that holds everyone back.
If I were to ask, how many of you are either busy writing or have intension to write your own DOS, BASIC, graphics driver, KERNAL, etc. in the near future.
I would have to raise my hand to most of the above...as time allows.
We're all writing these things in isolation and from scratch and even though code is shared via GitHub or similar, how often do you re-use other peoples code?
Probably not that often because it's not compatible with your hardware or has features that you don't want/need.
Lots to think about.
Andre