Well, if you follow that line of thought to the logical conclusion, you might as well not bother with the 6502 at all. After all, you could emulate 6502 code faster on a raspberry pi than you can run it on a real device, and you get bucketloads of RAM, mass storage, full hd graphics, USB interfacing, networking etc. for a lot less cost than you could build it yourself.

On the other hand, if you begin with the idea of building a system with a physical 6502 device and want to do your own system design, logic design etc. you end up with a different conclusion. Plus if you add in the idea that this is a "last in line" system, you may as well go the whole hog. $50 for a CPLD isn't cheap, but it's not a order of magnitude increase in total system cost.

It all depends what you want.

ok yea i get your point.
but 50 bucks is still a lot for a chip, even if it's used in just 1 system. that can easily double the cost of the whole thing.
it would be especially painful if you don't have the ability to desolder it in case the PCB is a bust or you want to use that chip in another project.

I have a decent collection of Compact Flash cards and the original IBM Microdrive (before we sold Hitachi all of our desktop related storage). The original Microdrive did use the CF Card format and connector, but was a Type II as it is thicker than a typical CF Card.

The Microdrive I'm using is NOT a Compact Flash format. It is physically smaller than a CF Card and does not require the CF Card socket. It has a very tiny 35-pin connector for a flat cable. See pic attached.



In testing, I'm finding the 6GB Microdrive is a bit faster than most of the CF Cards I have. It also supports multiple block transfers and I've implemented Write Caching in the BIOS which improves Block Write performance. Also, these can be found NEW for very reasonable prices... ~$20 for qty one. Note that these are 3.3-volt ONLY!

_________________
Regards, KM
https://github.com/floobydust

$50 for one EPM570!! I have several trays of these I bought a decade ago at salvage price I don’t remember anymore, but it couldn’t be more than $1 each—I’m a cheapskate so I doubt I’d pay $50 for 50 of them in those days. I’m watching floobydust’s project with great interest. I think EPM570 can take care of all I/O so what’s left is SMT 6502, RAM, and a mass storage to form a credit-card size SBC.
Bill

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

Bill, et al,

Years ago I built up a dozen mini headphone amps and mini DACs for audio use. These were designed by Ti Can and his website is amb.org.

Both of these neat little devices are housed in a Hammond 1455C801 extruded case. The PCBs are a standard Euro size. The mini DAC required 2 PCBs which were plugged together and slid into the case. The case size is: 80mm x 54mm x 23mm. Pics attached:






For my Pocket SBC, the upper PCB will contain:
W65C02S in QFP
SC28L92 in QFP
RAM in TSOP-44
Flash NAND in PLC44 (in SMT socket)
DS1501 in SOIC-28
EPM240T100 in QFP
SMT Clock oscillator
SMT Xtal for DUART
SMT Resistor pack
SMT caps for bypassing, etc.
SMT socket for Microdrive flat cable
10-pin JTAG connector (possibly in 2.0mm header)
Header connectors to lower PCB

The lower PCB will contain:
FTDI USB to UART SMT interface
5.0V to 3.3V SMT regulator
TL7533 Reset chip in SMT
DS1233 Panic (NMI) chip in SMT
Mini-USB connector for console
Mini barrel connector for 5V power
3 LEDs for indication
two momentary switches
one power switch
one header for second serial port
one header for GPIO (DUART port)
usual bypass caps, resistor, etc. (all in SMT)
Header connectors to upper board

Note: Microdrive will be shock-mounted to lower PCB. Both PCBs will be 4-layer.

Hope this is more clear in what my goal is for the Pocket SBC.

_________________
Regards, KM
https://github.com/floobydust

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

I've gotten much better with the tiny packages over the past few years. A new WX2 Weller setup with their Pico iron helps quite a bit, along with a large magnifier lens.

My next tool purchase will be a stereo inspection microscope with a ring light. That will give me a much clearer picture of what I'm doing. Beyond that, I'll probably look into a small reflow oven, depending on how this next project works out on soldering.

The Mini-DAC images posted earlier have some pretty small SMT components, and I used a standard magnifier with ring light to build 10 of them. I agree that getting older makes this kind of work more difficult

_________________
Regards, KM
https://github.com/floobydust

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

Instead of an oven, you might be interested in hot plate soldering. James Sharman had a video on it recently https://www.youtube.com/watch?v=nYzFj7fpsPI For PCBs smaller than 20cm squared, the fact that I don't have to store an actual oven in my workspace is pretty neat

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BB816 Computer YouTube series

Hi Adrien,

Yes, some time ago, I also looked into some hot plate solutions. Good link on the James Sharman video, thanks.

Being in South Florida, the A/C runs a lot, especially during the summer, so an open hot plate could be a bit difficult if it gets a cold draft. I've recently found one with a hinged cover, so you can "sorta" use it like an oven as well.

https://www.newark.com/quick/quick870/p ... dp/18X2885

This could be a possible solution, but I would likely fabricate a PCB holder so I can easily and steadily remove it without disturbing any of the parts while still hot.

_________________
Regards, KM
https://github.com/floobydust

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

Yea, you're right... it is on the pricey side. I may not get my $$ worth from it over time... hard to say.

I did find a better price on one of the popular reflow ovens.... and is located in NJ of all places (China West?).

https://www.ebay.com/itm/124250362274?e ... SwhUFfBAPa

There's also a handful of modifications out there for improvements. We'll see, still traveling this week.

_________________
Regards, KM
https://github.com/floobydust

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

I got one for $30, but had to put in an arduino and thermistor to control it. Works very well, even for BGA (!)

A smoke vent is for flux smoke. I don’t have it and need to open the door to my garage... Flux smoke is not very healthy, so its probably a good idea.

As for the original topic of memory paging:
I have tried to get my head around a MMU which does the same thing, although more complicated. I think 4KB page size makes alot of sense in that one can focus the effort to the higher 4 bits of the MSB. I do want to point out that you may want to have a way to «mask» those bits or have the paging system to ignore them (at some point). The reason is that you can then point to the page by one (or two) instructions and ignore page setting on the next instructions. It is more work hardware-wise, but makes things alot easier when programming.