XT-IDE on PCjr

Hardware questions and modifications

Re: XT-IDE on PCjr

Postby Brutman » Sun Apr 24, 2011 4:57 pm

I've been thinking .. yes, it hurts.

First, I've been playing with an old Legacy expansion chassis that had a 20MB MFM hard drive in it. The hard drive is shot. I'm really happy we are talking about newer IDE drives, not MFM drives, because they are frustrating as all hell.

This is going to sound crazy, but rather than gutting a Racore unit or trying to find a stand-alone ISA enclosure (none of which seem to match what we need), I'd like to make my own sheet metal enclosure. It requires access to a sheet metal break, drill press, and a few other tools, but a custom made enclosure has tremendous possibilities.

For features I think the following is doable:

  • 512KB SRAM. (Any SRAM is fast enough for a PCjr, including an 8Mhz machine.)
  • Another SRAM to bring us to 736K (it is easy to do)
  • IDE adapter (with the performance fixes)
  • 2 or 3 ISA slots
  • Power supply with fan, or a separate case fan
  • Internal tray for mounting a 3.5 or 2.5" hard drive
  • External bay for a 5.25" drive (or 3.5" drive with a standard adapter)
  • Parallel port (1 or 2?)
  • Clock and calendar (subject to finding a suitable chipset - should not be too hard)

The expansion chassis would be cable attached so it would have to connect to the last sidecar on your system. The expansion chassis could be above or below the Jr - it doesn't matter too much.

I think that the extra memory, IDE adapter, and parallel port and clock/calendar CMOS chip would fit easily on a small board. Two or 3 ISA slots would cover other things that are more complicated, like Ethernet or SCSI cards.

I dropped Ethernet from the design - not everybody needs it, and there are existing cards out there. The ISA slots take care of that.

Adding a parallel port or two would be a good thing. I don't know how to do this though. I imagine there is an IEEE 1284 chipset out there that might be obsolete that we can still find. I've been looking at Mouser for the last 45 minutes, but I really don't know what all the parts we would need are. (They have some obsolete parts in large quantities that might work, but the data sheets did not have a lot of detail in them.) If we can't put the parallel port on the custom card we could burn an ISA slot and use a generic card.

So, do you guys think I'm really nuts now?
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Re: XT-IDE on PCjr

Postby jmetal88 » Sun Apr 24, 2011 5:05 pm

I'd be down with that, as long as I can get an enclosure from you and I don't have to try finding the tools to make one myself. :lol:

Of course, I suppose my interest will ultimately be dictated by total cost. If it costs too much to produce, we should probably go smaller.
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Re: XT-IDE on PCjr

Postby Brutman » Sun Apr 24, 2011 5:28 pm

I don't see how we go smaller ...

Looking at my current system:

  • Two bi-directional parallel port sidecars
  • 512KB memory sidecar
  • Power sidecar
  • ISA bus adapter board
  • XT-IDE card
  • 20GB Maxtor hard drive floating around in space
  • Separate power supply for the hard drive

An expansion chassis takes care of *all* of that, and makes it more robust too. Right now everything is hanging off the outside of the machine; it's a disaster waiting to happen.

I think that getting rid of 3 or 4 sidecars, the adapter, a discrete IDE card, and getting the hard drive and power supply in a proper enclosure is a slam dunk. There are only two things bothering me now:

  • I can find generic Winbond Super I/O chipsets for the parallel port, but they are going to be impossible to solder by hand and I have no idea if we can use them. (They have a floppy controller, serial UARTs, game port, parallel ports, and other crap on them.)
  • I have access to people who know how to machine parts. I can't set up a production line though.

Mike
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Re: XT-IDE on PCjr

Postby jmetal88 » Sun Apr 24, 2011 9:31 pm

Well, here's a schematic of the original parallel port. If all else fails, we can duplicate that.

http://www.armory.com/~rstevew/Public/L ... c_wid.html

If we're willing to go with PLDs, we would probably cut the chip count down quite a bit. I'm reluctant to put more parts that need programming into the project, though.
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Re: XT-IDE on PCjr

Postby Lutiana » Sun Apr 24, 2011 9:48 pm

I am going to chime in here a bit late in the game and I read through the first 5 or 6 pages here so I may be a bit out of date.

I think that a sidecar would be a good idea. One that has IDE and RAM in it at the minimum. Ethernet would probably be next in the list (as others have said). I would have no problem sacrificing one of my simpler sidecars (just RAM or just parallel) to get these 3 or 4 things in one.

Personally I would use it with either a small CF card, a 1.8" drive or a standard laptop drive (all are low power). I would try to get into the sidecar and let them suck juice from the PCjr, or worse case add a 5V wall wart.

I would buy two of these in a heartbeat, and I can't see why I would need anything.
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Re: XT-IDE on PCjr

Postby Lutiana » Sun Apr 24, 2011 9:51 pm

jmetal88 wrote:If we're thinking about ISA, how about one of these as an enclosure?

http://www.arstech.com/cat-Enclosures-enclosures.html

I'm not sure it's an exact fit for what we want, but something could be done with these.


I have worked with one of those before. A USB to ISA thing. The case looks good, but all it is plastic and in the end is a bit flimsy. I don't think I'd recommend them.


EDIT:
Ok, finished reading the rest of the posts. I still think a 3-in-1 sidecar would be ideal, but I think Mike's suggestion of a single enclosure with IDE, RAM, Clock, Parallel, 2 ISA and mounting points would be pretty awesome and could be far more functional. If we are going to do it, we may as well add in 2 parallel ports. Is serial possible too? That would add modern-ish mouse functionality or other serial devices (can't think of any right now).

We could make the enclosure have roughly the same foot print as the PCjr (14"x11 3/8") and tall enough for standard ISA cards (5 1/4") or less if we made it so the ISA card mounted sidways, could be as small as about 3" or 4" depending on the PSU. This would go nicely either under or on top the the original PCJr with a pigtail on the side connecting the two.
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Why Re-invent the wheel

Postby Lutiana » Mon Apr 25, 2011 2:07 am

I was thinking more about the second eclosure and the specs we would be looking for:

1. External 5.25" Bay
2. Internal 3.5" Bay
3. Its own PSU and cooling
4. Slots on the back for ISA cards (2 or 3)

And it occured to me that specs read pretty much like a standard PC case. So why re-invent the wheel? Just look for a micro ATX or iTX enclosure and that is inexpensive (or less expensive than a custom fabrication of a case). If we built the board to fit the mATX standard case layout, then the options for chassis are limitless, you could even use an old case you have lying around.

I found this one for about $12 w/o the PSU, its a bit bigger than I'd like and we would not need the external 3.5" bays, but it is a fairly good example of what I mean.
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Re: XT-IDE on PCjr

Postby Lutiana » Tue Apr 26, 2011 8:27 pm

I've been thinking. Do we really need the RAM upgrade on this thing? I mean most people allready have a sidecar and if they don't jmetal88's internal upgrade would probably be a better option.

This would give us more space on this PCB. So maybe we go back to the idea of a side car with IDE, Network and/or Parallel. What do you guys think?>
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Re: XT-IDE on PCjr

Postby jmetal88 » Tue Apr 26, 2011 8:42 pm

Well, at first I was up for the all-in-one thing (I don't really care what happens with my RAM upgrade - I'm doing it for my own benefit), but now I'm starting to think that maybe we should try to do a board that could fit inside an external hard drive enclosure, and get power from that, with just the IDE chipset on board. Then connect to the PCjr via ribbon cable to the sidecar bus. I guess I just have an aversion to 'big' add-ons. I like things nice and inconspicuous. :)
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Re: XT-IDE on PCjr

Postby Brutman » Tue Apr 26, 2011 9:09 pm

My personal preference is to avoid the daughterboard solutions. The jrHotshot was an elegant design, and PC Enterprises copied it when they did their jrExcellerator. So did Legacy. But ...

  • It requires you to have a socketed 8088. Some PCjrs have those soldered down.
  • It draws power from the internal power supply card, which is marginal for the task. (Although an SRAM chip helps that a lot.)
  • It contributes to heat buildup under the floppy drive tray.

A sidecar solution works, but we have to cannibalize a sidecar to get a shell and connectors, and we still might have a power draw problem. One nice thing we can do for a sidecar solution is to use a "Disk On Module" (Flash device), which would fit easily in the sidecar and require minimal power. That would be nicer than having a ribbon cable going to an external drive and power supply.

Everybody needs a memory upgrade solution. The most common form is the upgraded sidecar, so putting a little extra logic on an IDE sidecar helps the power budget by eliminating the need for a memory sidecar. (And the memory sidecar can serve as the donor for the shell and connectors.) Racore users probably aren't too keen on this, as the Racore already provides extra memory.

The external enclosure that does everything is a massive solution - it nearly replaces everything, and includes slots for ISA cards. Those slots are more useful than you think - besides the Ethernet cards that I love so much, you can also stick in a dual printer port card that has bi-directional and EPP capability for those extra devices.

There are so many options .. it's hard to settle on one. Hence the discussion.
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