VOGONS


First post, by delinthe

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So I bought an 8-bit network card with an RJ-45 connector, woo! It's arriving today, further woo! It dawned on me that I don't have a viable way to get a packet driver onto the XT without the network card being online (Hooray for circular problems.) I spent some time going through this forum, googling, redditing and saw a couple potential avenues and would love some help figuring out the path of least resistance here.

My initial thought was that I could transfer the file over a serial connection. I don't have a serial port on any of my modern computers, but as a network engineer I do have a ton of USB to Serial adapters utilizing the PL-2303 chip. I read in a post however that this doesn't work due to the voltage levels on serial port on the XT side. I read a little bit of the RS-232 standard and it sounds like the voltages are from -15 to -3 on the low side and 3 to 15 on the high side. Since the operating voltages are in the specification I would hope that there would not be potential for damage in either direction. I'm guessing the only problem would be perhaps if the XT was operating at +12 -12v it wouldn't see the 3+.3 or +5 volt signaling from the USB adapter as hitting the required high voltage mark to signal a 1. Let me know if I'm wrong and if there is actually potential to fry something because I want to avoid that at all costs.

There is of course also the parallel port on the XT but I don't have parallel ports on my modern computers, nor do I have adapters to work with parallel.

There is the 5.25" floppy drive, but I have no floppy disks or another 5.25 floppy drive. It also seems unlikely that I could possibly find a PCIE floppy drive controller and make one work in a modern Windows 10 environment.

I have a drawer full of Arduinos, Raspberry Pis, and various other SBCs and development boards. It's possible that I could with a lot of work have something act as a level-shifter if absolutely need be. Or alternatively use the SBC itself to store and transfer files to the XT. I'd love to avoid this solution because it sounds like something that might take weeks to accomplish, especially if I wind up needing to order additional components to step voltages down (buck converter) and up (MOSFET). I'm not even sure this would work because apparently larger voltage shifts require you to reduce signaling speed. Most of the commercially available level-shifters I'm seeing have a swing voltage of 1.7-3.3V and I'm kind of guessing I may be looking at a 7V swing.

The last input method I've been able to think of is the keyboard. Perhaps I can somehow bang out a quick direct communication method using the network card and basic/ASM. Though honestly... I think that would be pretty far beyond my current abilities with ASM.

Reply 1 of 11, by maxtherabbit

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If you want to make a habit of working on 80s PCs you really need a 90s or early 00s PC to act as a go between.

Reply 2 of 11, by Predator99

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Serial connection is not a bad idea if your XT can boot DOS. Transfer should work with the copy command.
RS232=RS232...never heard of different voltages.

Otherwise I would suggest a Gotek or a IDE-CF adapter with IDE-controller.

Reply 3 of 11, by chinny22

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If your daily PC still supports floppy disk drives Gotek is good value, you can use the one between the 2 PC's or get one for each
If your daily PC doesn't have a FDD connector you can get USB floppy drives but these are all 1.44mb 3.5 types so will need a drive in the XT as well

Depending on what type of HDD the XT has you can plug it direct to your pc with a USB to IDE cable or CF/SD card reader.

but yeh you really want either the ability to create something thats bootable or plug direct to the modern PC, casue you know that one day its just not going to be able to load an OS

Reply 4 of 11, by delinthe

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Thanks everyone, I've decided to take two approaches! I ordered an XT-IDE, and a DE9 to DB25 Null modem cable.

So I see that i can use the copy command and send something to a com port in windows 10 using syntax like copy xtidecfg.com com3 /b what do I have to do on the receiving computer (The IBM XT in this case) to have it wait for serial data and then dump that into a file? I've spent a few hours googling but I've had no luck finding the answer to that question. So much old dos knowledge exists only in out of print books these days! I looked through my both my IBM DOS and Guide to Operations Personal Computer XT manuals but didn't see any information about copying files via serial in either. I did verify that I can use similiar syntax on the XT in PC DOS 3.30 copy testfil.com com1 /b which just gives me the error

write fault error writing device COM1

which I assume is because i'm not choosing a valid configured com, or if I am there is nothing hooked up to it. But the fact that it allows the syntax targeting the com seems like a good sign.

Reply 5 of 11, by Caluser2000

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You should be able to use later Dos interlnk/inerserv or DRDos's filelnk programs to do the transfers.. Or via a terminal emulator between systems.

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Of course, as always, I'm open to correction...😉

Reply 8 of 11, by jakethompson1

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Does anyone know if it's possible use Cassette BASIC to get an assembly language program in memory and jump to it? It's something I've never looked into.
This is possible on an Apple II (something involving negative line numbers if I remember right), and ADTPro uses it as part of the bootstrapping process.

Reply 9 of 11, by delinthe

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I was able to type out a BASIC receive only Kermit program in basic that I found on the Columbia University website.

ftp://ftp.kermit.columbia.edu/kermit/mskermit/msbrcv.bas

After this I setup a db25 to de9 null modem cable from my windows 10 computer to my IBM XT using a PL2303 USB to Serial adapter. On the windows side I used Kermit for Windows Version 0.85. I configured the baud rate to 1200, word length to 8, parity to n, stop bits to 1, and left off both handshake methods XOn/XOff and Hardware. I also set the packet size to 40 for both receive and send. After this I was able to transfer the real Kermit for DOS to the IBM XT. At that point I was able to increase the baud rate to 9600 and successfully transfer other binary files to the IBM XT.

Thank you everyone for your help getting this IBM XT bootstrapped!

Reply 10 of 11, by Jo22

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delinthe wrote on 2020-05-22, 13:04:

[..] port on any of my modern computers, but as a network engineer I do have a ton of USB to Serial adapters utilizing the PL-2303 chip.
I read in a post however that this doesn't work due to the voltage levels on serial port on the XT side.
I read a little bit of the RS-232 standard and it sounds like the voltages are from -15 to -3 on the low side and 3 to 15 on the high side. Since the operating

Well, yesn't. It's true that a real serial ports uses -12v to +12v, while USB-Serial adapters mainly use TTL levels 0v, +5v (+3,3v).
However, the real serial ports are tolerant enough to handle TTL levels usually. So pure data transfer usually works.
I tried this with FileMaven, DOSBox, an old PC, a null-modem cable and a PL2303 serial adapter..
https://www.youtube.com/channel/UCM_rzw6WcXib … query=Filemaven

What usually not works is controlling logic circuits that are built out of discrete parts (relais, transistors, opamps etc).
These were made with a specific voltage range in mind and don't work out-of-box with 3.3v/5v and thus USB-Serial adapters.
Especially circuits with a comparator do fail, because they need to "swing" from negative to positive (rail-to-rail operation).
The HamCom modems from the amateur radio scene which use 741 IC fall into this category, for example.
https://www.qsl.net/iz7ath/web/03_digital/03_hamc/hc_eng.htm
https://www.youtube.com/channel/UCM_rzw6WcXib … earch?query=741

However, if you add one or more MAX232 ICs in an adapter circuit, you can use a modern PC or MAC to interface with an old device through the PL2303.
Alternatively, you can modify such circuits to use a pair of 9v batteries.
If you connect them in serial, one end will be positive (+9v), the other negative (-9v) and the middle will be "0v".
Anyway, please always double check the voltages before you try!
https://www.qsl.net/iz7ath/web/home_eng.htm

Good luck! 😀

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Reply 11 of 11, by jmarsh

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Still baffles me why 9V batteries don't have something like a raised bump in the middle to prevent them being connected to each other.