XT-IDE on PCjr

Hardware questions and modifications

Re: XT-IDE on PCjr

Postby jmetal88 » Tue Mar 15, 2011 6:50 pm

I've also heard good things about the Willem programmer:

http://cgi.ebay.com/PCB5-0-Willem-EPROM ... 3429wt_936

There are other auctions selling it cheaper, but I like to buy these things from inside the USA.
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Re: XT-IDE on PCjr

Postby Brutman » Wed Mar 16, 2011 6:33 pm

I've heard of the Willem programmers before, but when I went looking at their web site it seemed to be taken over by people who make money on bogus searches. So I'm still hunting around for more information about them and others ...

(No need to reply. Google is my friend here. :-) Unless you have something that you know and love very well ...
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Re: XT-IDE on PCjr

Postby jmetal88 » Sun Mar 20, 2011 12:22 pm

I've decided I like the second DIY one I posted best - the Blake Foster design. I've gotten rid of the Windows DLL he was using in his program and compiled it for 16-bit DOS. I'm not sure if it works yet, because I haven't built the hardware. I'm also adding a 7475 to the design so I can kick the PPI and the EEPROM into read mode whenever they're not in write mode, which I'm hoping will allow me to read the chip back, provided the programmer is attached to a bidirectional parallel port.

EDIT: Also, I'm adding in the other two address lines, so I can program the 32kx8 EEPROMs as well as the 8kx8 EEPROMs.
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It runs!

Postby Brutman » Sun Mar 20, 2011 12:27 pm

It is a little bit of a hack at the moment, but it has been up and running for an hour now. Here are the details:

  • XT-IDE adapter running a slightly modified BIOS on a PCjr bus to ISA bus adapter
  • DOS 3.3
  • JrConfig.sys
  • 20GB Maxtor hard drive

DOS 3.3 isn't a great OS to test something like this because it only supports partitions up to 32MB in size, but for testing the function of the card it is all one needs. I was able to boot the machine to DOS from the floppy drive, FDISK and install DOS on the drive. The machine boots DOS from the hard drive now directly. I added JrConfig to reserve the slow memory and get my speed back; it is not needed.

The speed isn't great. The BIOS does PIO to the drive; measuring with a stopwatch reveals reads are getting about 85KB/sec and writes writes are getting about 64KB/sec. This is comparable to the same adapter on an XT. There is a small modification that one of the members discovered to put the two data registers back to back, allowing for much faster speeds; we can do that easily. Memory mapping the registers would work even better. And finally, for those of us with V20s the BIOS can use a minor tweak that would improve things a lot too.

I'm going to let the glow wear off and then we need to start thinking about next steps. Before the end of the day I'll test this in the MattC bus adapter. If that works that means that anybody with an existing XT-IDE adapter can flash a new BIOS on and start using the XT-IDE on their Jr.


Mike

Late edit: Matt, it works with your original ISA bus adapter . Don't cut those XT cards in half! :-)
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Re: XT-IDE on PCjr

Postby jmetal88 » Sun Mar 20, 2011 1:19 pm

Awesome! Out of curiosity, which programmer did you end up using?
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Re: XT-IDE on PCjr

Postby Brutman » Sun Mar 20, 2011 1:22 pm

I haven't even ordered the programmer yet - I was really anxious to do this!

The XT-IDE uses an 28C64 which can be reflashed right from the card using a DOS utility. I modified the code to put a 'chicken switch' in - if it detected the BASIC cartridge at E800:0000 it would exit without loading. Otherwise, it would try to load and run. This protects me if I put a really bad image on the EPROM - I can insert the BASIC cartridge, boot from floppy, and reflash the EPROM if I do something horribly wrong. (I'll remove the BASIC cartridge check later on after I have a programmer.)

There is a Willem derived design that MCUMall in Canada sells. It looks a bit more industrial strength than the standard Willem. There are some Genius models that were recommended to me too; I have to figure out which one to get still.
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Re: XT-IDE on PCjr

Postby Brutman » Sun Mar 20, 2011 4:07 pm

And the obligatory picture ...

Image

(Go to http://brutman.com/pics/XT-IDEjr_large.jpg for the full sized picture.)
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Re: It runs!

Postby MattCarp » Mon Mar 28, 2011 11:31 am

Brutman wrote:The speed isn't great. The BIOS does PIO to the drive; measuring with a stopwatch reveals reads are getting about 85KB/sec and writes writes are getting about 64KB/sec. This is comparable to the same adapter on an XT. There is a small modification that one of the members discovered to put the two data registers back to back, allowing for much faster speeds; we can do that easily. Memory mapping the registers would work even better. And finally, for those of us with V20s the BIOS can use a minor tweak that would improve things a lot too.

I'm going to let the glow wear off and then we need to start thinking about next steps. Before the end of the day I'll test this in the MattC bus adapter. If that works that means that anybody with an existing XT-IDE adapter can flash a new BIOS on and start using the XT-IDE on their Jr.

Late edit: Matt, it works with your original ISA bus adapter . Don't cut those XT cards in half! :-)


Of course! :)

Actually, thanks for the update! This is awesome! I'm excited about booting from hard disk, and IDE no less. I can now use this as a talisman to keep from being haunted by the $30 eBay auction of the Xebec controllers...!


On the programmer, if possible, look for Motorola MCM68766L EPROM support. That's the EPROM used in the IBM Fixed Disk Adapter mod. I didn't see it in the Willem specs. It's an old chip, so it may not be supported. It may be easy to update a config file on a current programmer to support it. Anyway, something to know - may not matter in the end.
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Re: It runs!

Postby Trixter » Thu Mar 31, 2011 11:33 am

MattCarp wrote:
Brutman wrote:Late edit: Matt, it works with your original ISA bus adapter . Don't cut those XT cards in half! :-)


Of course! :)


Wait, what? Can someone give me some context to understand the above?
You're all insane and trying to steal my magic bag!
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Re: XT-IDE on PCjr

Postby jmetal88 » Wed Apr 06, 2011 3:07 pm

Hey, I started messing around with the XT-IDE schematic in KiCad and replaced the ISA connector with a 60-pin connector with the PCjr sidecar pinout. If I can get some accurate measurements for a sidecar PCB, it would be pretty simple to draw up a PCB that you could put in (and use connectors from) a dead LPT sidecar or something. Then you'd just need an enclosure for the drive.

I might try to measure the board from my LPT sidecar when I get home this weekend if nobody has accurate measurements already. Doesn't have to be done this way, but since I still have that little plastic side panel for my PCjr, I'd love to be able to leave it on.
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