XT-IDE on PCjr

Hardware questions and modifications

Re: XT-IDE on PCjr

Postby jmetal88 » Thu Apr 14, 2011 12:32 pm

I could try putting both on the board. That way, nobody needs an adapter for anything. :)
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Re: XT-IDE on PCjr

Postby Vorticon » Thu Apr 14, 2011 2:12 pm

Brutman wrote:If I'm not commenting at length, excuse me - I'm distracted. (Announced my resignation from IBM yesterday.)


Sorry to hear about that. Hopefully better opportunities will come your way.
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Re: XT-IDE on PCjr

Postby jmetal88 » Thu Apr 14, 2011 2:15 pm

Alright, I'm autorouting a version of the board with both connectors on it right now. I took the memory upgrade off the board, though. There's still room for it, but I'd really rather see my CPU socket memory upgrade working before this (and having that would make memory added to this redundant).

Besides, if someone actually does want to tackle a packet driver, that would leave more room for an ethernet controller on the board. :) I'd be more comfortable if someone besides myself came up with a schematic for the ethernet controller, though. I'm not really comfortable that I have the proper knowledge and skill set to come up with a working one right now. Adding someone else's schematic to the board is well within my capability, though (providing the components fit).
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Re: XT-IDE on PCjr

Postby Brutman » Thu Apr 14, 2011 3:09 pm

Just a few quick notes:

A lot of the "embedded" Ethernet chipsets that we would get today already have packet drivers available for them. Part of the selection process should include whether or not a packet driver exists already. I can write a packet driver from scratch, but having an existing one is much easier. Personally, I really want Ethernet .. but you all know my bias there. ;-0

I like the memory on the sidecar slightly better. We're going to have problems with Jrs out there that have the 8088 soldered onto the board. Removing the board and desoldering is not going to be feasible for a lot of people. I also hate removing the floppy drive tray - the damn friction fittings always break. So while the daughterboard is a nice, neat looking solution, since we have to have a sidecar for the IDE portion we might as well put the memory there too and not mess with the motherboard or floppy tray.

The XT-IDE design as we have it now is slow and nasty. Don't put too much into designing and routing it. At a minimum I want to swap some address lines going to the latch around so that we can have the two 8 bit latches as successive I/O port addresses. That would enable one 16 bit read or write to a port, instead of the two 8 bit reads to two separate ports we are doing now. That minor change speeds the throughput by at least a factor of 3. If we take a further step and memory map it, then we improve it by another 20%. Lastly, the XT-IDE design is 'borrowing' memory that doesn't belong to it that might cause us problems. The solution is to add a small amount of memory (1KB or less) in the ROM address range right after the XT-IDE ROM, but that's a significant design change.

Anyway, like I said, don't run ahead too far .. The XT-IDE is good for what it does, but with a few minor tweaks it could be much better.


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Re: XT-IDE on PCjr

Postby Brutman » Thu Apr 14, 2011 3:09 pm

Vorticon wrote:
Brutman wrote:If I'm not commenting at length, excuse me - I'm distracted. (Announced my resignation from IBM yesterday.)


Sorry to hear about that. Hopefully better opportunities will come your way.


Don't worry - it's all goodness. After 18 years there it's time to start a new adventure ...
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Re: XT-IDE on PCjr

Postby jmetal88 » Thu Apr 14, 2011 3:33 pm

Oh, I'm not running ahead by a long shot. :lol:

Just having the autorouter show me how the board will come out. With the way I have KiCAD set up, modifications are simple to make.

Here's an embedded ethernet controller that looks like it would be really easy to interface to the PCjr, but I have no idea if a DOS packet driver exists already:

http://search.digikey.com/scripts/DkSea ... 36-1312-ND

Only problem is it's tough to solder surface mount stuff sometimes. Guess it depends on who's putting the boards together after they're printed, though.
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Re: XT-IDE on PCjr

Postby Brutman » Thu Apr 14, 2011 3:43 pm

Ok - just want to make sure we're not doing extra, speculative work ..

The two chipsets I had in mind are from Crystal Semiconductor and Realtek. The numbers escape me at the moment but they are well known and often appear on the Apple ][ and C64 ][ Ethernet boards. They are big parts though; most of us won't have the skill to be able to solder them.


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Re: XT-IDE on PCjr

Postby jmetal88 » Thu Apr 14, 2011 4:30 pm

Hmm, Digi-Key has a Crystal chip that's supposed to directly interface with an ISA bus, but there are DMA pins on the chip, so I wasn't sure it would work. I guess I should probably look at the full datasheet to see if connecting those pins to the computer is actually necessary.

EDIT: Hmm, actually, it looks like the data bus is 16 bits wide on this particular chip. Probably not a good choice then.
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Re: XT-IDE on PCjr

Postby MattCarp » Thu Apr 14, 2011 5:03 pm

Vorticon wrote:
Brutman wrote:If I'm not commenting at length, excuse me - I'm distracted. (Announced my resignation from IBM yesterday.)


Sorry to hear about that. Hopefully better opportunities will come your way.


Do not - I repeat, do not - get into the PCjr uprgade business.
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Re: XT-IDE on PCjr

Postby MattCarp » Thu Apr 14, 2011 5:11 pm

jmetal88 wrote:Hmm, Digi-Key has a Crystal chip that's supposed to directly interface with an ISA bus, but there are DMA pins on the chip, so I wasn't sure it would work. I guess I should probably look at the full datasheet to see if connecting those pins to the computer is actually necessary.

EDIT: Hmm, actually, it looks like the data bus is 16 bits wide on this particular chip. Probably not a good choice then.


The Cirrus 8900 is fairly common. It works on the 8-bit ISA bus.

DOS drivers may exist: http://www.nodevice.com/driver/company/ ... Logic.html

This link includes drivers and the source code!

http://www.helpdrivers.es/Cirrus_Logic/ ... iver_81090

This link to drivers seems to have a DOS packet driver for the 8900:

http://www.lostmydrivers.com/network-dr ... 0-dos.html
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