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If the idea of the project is to prove that you can do it on that aged CPU, just for fun, I guess you'll have to do the big work of implementing a USB host.
If you have a problem that requires a solution, one way or the other, you could use one of the tinier Arduions as a relay: Your old CPU talk through an RS232 interface to an Arduino that acts as a USB host through e.g. The Arduino USB Host Shield[^], forwarding the data to the USB devices. Making the two boards cooperate is a nice challenge as well: You will have to do some protocol development to synchronize activities under two quite different OSes. Not too hard, but well above what you would give as a homework assignment to a freshman CS student.
I am sure that there are similar Raspberry Pi solutions, but Pi solutions tend to be more ambitious, larger, more expensive. Arduino solutions are often more limited, but much simpler to handle if all you need is a very simple solution.
If you are a soldering iron person: That Arduino web page refers to the MAX3421E[^] chip on the shield. You may of course try to get hold of one of those and add to your setup, avoiding the complexities of an Arduino. You can probably pick up a lot of useful info from the Documentation tab on the Arduino page (such as the diagram for the shield).
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CodeWraith wrote: Remember what Commodore did with the C64's floppy drives?
I had a TRS-80 Model 100, along with the external floppy drive. The drive used RS-232 at a whopping 19.2K baud to talk to the drive, which held an amazing 100K.
Software Zen: delete this;
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Converters like the one mentioned are typically only for connecting slave devices to host computers. If you are trying to be the host and use a memory stick, you need a USB Host or OTG peripheral.
Something along the lines of the Arduino Host shield if you want a pre-made solution.
Arduino USB Host Shield[^]
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I think it's meant to be used the other way. You talk to the usb part and out comes TTL
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didi dodidi didi dodidi dodi do do didididi didi dodi dodido dido dodi dodidodo dodido dodi di didodo
dodo dododo didodi dididi di dodidodi dododo dodidi di dido dodi dodidodo dodo dododo didodi di
(The secret language of ancient hackers.)
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Have you seen Mark of RetroClinic's DataCentre (RetroClinic DataCentre - USB on your Beeb[^]) for the BBC Micro? The DataCentre is discontinued, but I expect he would be willing to discuss any questions you have.
I seem to recall that one of the big issues was the Beeb's 16-bit address bus, which meant only accessing a fraction of, say, an SD card's capacity, but I have no idea what the solution was.
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USB is complicated. Trust me. I would highly discourage you to implement your own.
That said, the protocol you're looking for is the USB Mass Storage CDC (Common Device Class). You're probably going to have to toush USB Attached SCSI as well.
If you want to do that though, this CH340 won't do, because it is a USB device and not a host. You'll need something with either a USB ROOT hub (like a RasPi), or USB OTG (I heard some AT90's and PIC16F's are capable of this, but I never found anything like that, so dunno).
You also don't "select" devices per se. When a USB device is connected, the USB hub sends you (the ROOT hub) a message. Let's say, it was hub #5. Then you instruct said hub to reset it. This will make the newly attached device assume an address of "5.0". Now, you send a GET DESCRIPTOR followed by a SET ADDRESS to USB address "5.0.0", which is the CONTROL endpoint of the new device. In SET ADDRESS, you give it a permanent address that it can use moving forward.
Now, why did I say you don't really "select" devices? Because, even though you can address individual devices, all attached USB devices will hear the ROOT's messages, and it is up to them to decide whether to activate or not. If you misconfigure a device and cause an address collision, you're screwed.
I could go on and on about USB, but I think you get the point: Don't Implement Your Own.
For your purposes, I'd use a SD/microSD card instead, as these can be used in SPI transfer mode, which is a cakewalk to implement, as opposed to the pain-in-the-backyard you're gonna have if you try to implement a USB host yourselves.
"I don't think about dying. It is the last thing I want to do. " - theoldfool
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Thanks. Upgrading an old computer is not easy and I'm still looking in all directions to see what is reasonable and what is not. Actually I'm not really upgrading it, but restoring it to its original condition and then build a new one with the upgrades.
SD in SPI mode is also possible, but the processor has no real SPI port. however, it does have a few microcontrollerish I/O signals. These already are doing triple duty as bit banged RS232, bit banged cassette tape I/O and bit banged sound generation. Back in the day, be even did digital sound recording and playback with them.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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If I had a 3D printer, could I print myself a stack of $100 bills? The stack doesn't have to be high. A foot or two will do me just fine. 
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The treasury will print you a nice set of handcuffs to go with it.
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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The Treasury doesn't worry me, but the Secret Service - ooh boy! 
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They're the enforcement arm of the treasury, love. =) Little known facet of how the US is structured.
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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As long as they let you print a handcuff key. /trollface
Did you ever see history portrayed as an old man with a wise brow and pulseless heart, weighing all things in the balance of reason?
Is not rather the genius of history like an eternal, imploring maiden, full of fire, with a burning heart and flaming soul, humanly warm and humanly beautiful?
--Zachris Topelius
Training a telescope on one’s own belly button will only reveal lint. You like that? You go right on staring at it. I prefer looking at galaxies.
-- Sarah Hoyt
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Why print dollar bills? Print a gold bar itself. Or a Platinum object.
Maybe some 3D printers do alchemic transformations.
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Quote: Print a gold bar itself
Good point! Do you have a 3D printer? Wanna go into a partnership?
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Yeah, shared losses are only half the losses. 
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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I don't have a 3D printer, but about 25 years ago, had seen a STL (Stereolithography) printer, which did something called layered manufacturing using a polymer. I guess today's 3D printers are an evolution of these.
Anyway, my footnote mentions about alchemy, which was supposed to have been practiced by our ancient people, but was systematically destroyed over time.
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Amarnath S wrote: Maybe some 3D printers do alchemic transformations.
Can't I do that with some clever XSLT?
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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That would actually work with a printer that can print metal objects. The problem still is that that filament, powder or whatever the printer uses contains real gold and probably is more expensive than buying that gold bar in the first place.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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but imagine the stuff you could make tho. puts jewelers on the next level. 
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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You are too late with your idea. Just upload your 3D file and pay the bill: Gold 3D Printing Material Information - Shapeways[^]
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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You could legally print yourself a cheque.
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Quote: You could legally print yourself a cheque
OK, can I please have your bank account info?
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phht, print bitcoins
- nobody really knows what a real one feels like but there's pictures on the net.
1 bitcoin currently at > $7000 (USD). not bad profit for a couple of bucks of metallic printer paste.
take a trip to NY - the capital of fast money greed
how hard would it be to find people dumb enough to buy your bitcoins 'at a discount, say $6000.'
- if they are reluctant show them the pictures on the internet,
- let them bargain you down to $5k
- tell them you need cash because the vending machine is out of change or for a taxi.
this internet has become nothing but fake news.
... time to fix it, time to get back to the fax!
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James, for just $15 an hour, and moderate encouragement, will write you a backtracking recursive descent parser suitable for parsing a modern programming language for less than the cost of using a parser generator tool that cannot parse such languages anyway.
James requires downtime for sleep, recreation, and "family"
Even still, James' parser deliverable will be about the same in terms of scheduling as if you were using a generator tool and refining a grammar input spec. 
When I was growin' up, I was the smartest kid I knew. Maybe that was just because I didn't know that many kids. All I know is now I feel the opposite.
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