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 Post subject: Re: Memory Paging
PostPosted: Sun Jul 31, 2022 1:49 pm 
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Proxy wrote:
oof, at those prices it seems way more feasibly to get a high end STM32 Microcontroller and just emulate the decoding logic with it.


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.


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 Post subject: Re: Memory Paging
PostPosted: Sun Jul 31, 2022 2:16 pm 
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kernelthread wrote:
Proxy wrote:
oof, at those prices it seems way more feasibly to get a high end STM32 Microcontroller and just emulate the decoding logic with it.


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.


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 Post subject: Re: Memory Paging
PostPosted: Sun Jul 31, 2022 3:12 pm 
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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.

Attachment:
IMG_2953.JPG
IMG_2953.JPG [ 2.39 MiB | Viewed 727 times ]


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!

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 Post subject: Re: Memory Paging
PostPosted: Sun Jul 31, 2022 4:07 pm 
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$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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 Post subject: Re: Memory Paging
PostPosted: Sun Jul 31, 2022 6:07 pm 
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Proxy wrote:
...i'm usually really scared of SMT, not because of the soldering (except those SOJ packages), but because i don't have any way to desolder them again, so once i put them on a PCB they're basically gone.

SMT parts can be readily desoldered with an ordinary heat gun. I've salvaged SRAMs in this fashion.

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 Post subject: Re: Memory Paging
PostPosted: Sun Jul 31, 2022 6:33 pm 
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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:

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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.

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 Post subject: Re: Memory Paging
PostPosted: Sun Jul 31, 2022 10:43 pm 
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floobydust wrote:
For my Pocket SBC, the upper PCB will contain:
W65C02S in QFP
SC28L92 in QFP
RAM in TSOP-44

You can solder those dinky packages? :shock:

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 Post subject: Re: Memory Paging
PostPosted: Tue Aug 02, 2022 6:36 pm 
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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 :shock:

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 Post subject: Re: Memory Paging
PostPosted: Tue Aug 02, 2022 8:36 pm 
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floobydust wrote:
Beyond that, I'll probably look into a small reflow oven, depending on how this next project works out on soldering.

About seven years ago, I embarked on reflowing, just for grins. I did get a workable setup going, but lacking a stencil to carefully apply the solder paste, I had bridges, some of which were under a part—no way to fix that!

I haven't done anything with it since, but when I had the PCBs for POC V1.3 made, I also ordered a stencil. I'm currently stuck on some problems with POC V2.0, so I might set it aside for a while and see if I can build a copy of V1.3 using reflow. All of the SMT parts on V1.3 are SOIC, which, in the past, I could manually solder. With my vision having significantly deteriorated in the last several years, placing the parts is a not-insurmountable challenge, but soldering them... So V1.3 would be a good guinea pig for getting back into reflow, since it is a working design.

QFP, on the other hand, is out of the question. :(

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 Post subject: Re: Memory Paging
PostPosted: Tue Aug 02, 2022 10:32 pm 
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floobydust wrote:
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 :shock:


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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 Post subject: Re: Memory Paging
PostPosted: Wed Aug 03, 2022 2:18 am 
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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.

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 Post subject: Re: Memory Paging
PostPosted: Wed Aug 03, 2022 5:55 am 
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floobydust wrote:
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/preheatreflow-hot-plate/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.

That thing is expensive! You can get a decent toaster-oven big enough to hold a standard ATX motherboard for less than 100 dollars, complete with digital temperature control and a fan to keep the air moving for even heating. Here's what I got—purchased from Walmart for about $80 in late 2015:

Attachment:
reflow_oven.gif
reflow_oven.gif [ 1.97 MiB | Viewed 597 times ]

As for handling your finished assembly, you need to allow the PCB to cool down in the oven. If you pull the board out of the oven while it’s still near reflow temperature you may damage parts from thermal shock. What I did during my reflow experiments was after I had reached peak temperature (~450° F) and held it for 30 seconds, I shut off the oven, waited for about a minute and then carefully opened the door to let things cool down. The finished PCB was safe to handle in about five minutes.

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 Post subject: Re: Memory Paging
PostPosted: Wed Aug 03, 2022 1:33 pm 
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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.

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 Post subject: Re: Memory Paging
PostPosted: Wed Aug 03, 2022 8:06 pm 
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floobydust wrote:
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.

Some strange descriptions for that oven. "Welding area?" They using stick, MIG, TIG or oxyacetylene? :D "Smoke vent?" Well, I sure hope the PCB assembly isn't smoking after reflow! :lol:

Jocosity aside, it still seems extravagant to me for hobby purposes. If I were producing multiple PCB assemblies for sale this oven might make sense, since I wouldn't have to babysit the process for each board. For hobby use, I can get a decent toaster oven and have $150-$180 left to spend on other things.

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 Post subject: Re: Memory Paging
PostPosted: Thu Aug 04, 2022 6:17 am 
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BigDumbDinosaur wrote:

That thing is expensive! You can get a decent toaster-oven big enough to hold a standard ATX motherboard for less than 100 dollars, complete with digital temperature control and a fan to keep the air moving for even heating. Here's what I got—purchased from Walmart for about $80 in late 2015:


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.


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