PEX Revisited Part III

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Joined: Jun 1 2004
Posts: 67
Hi, It actually based on a

Hi,

It actually based on a blank one that Trag had left over from when he manufactuered some for Beige G3s... so the board is already done, it's a case of soldering all the components on.

It's a 4-layer design, and a design file is available from Trag.

I've asked Trag if he had any more spare ones, but he said this is the last one left - although there might be a way of finding some more... will PM you with his details...

James.

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Joined: Aug 22 2008
Posts: 9
Any news?

If this thing has been set up so it can actually be _used_ to the full potential for which it was designed, that would be worthy of earning you a medal!

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Joined: Jun 1 2004
Posts: 67
News...

So far the project is on the back-burner. Trag is currently assembling a flashable copy of the ROM SIMM from the Digibarn machine.

When this has been done I'll be trying to get it boot OS X again.

On the 68kMLA forum Mark Crutchfield has posted the follwing:

Quote:

I have had one of the PowerExpress prototypes for 4 or 5 years, so I thought I would provide a link to my page about it:

[link]http://www.isellmacs.com/macsystems.htm[/link]

It's interesting to note that as his machine is probably the one that would have been mass-produced, or an extremely late testing prototype, that he notes that all of the customs chips have been removed (Denali /99/Radical). This would likely mean that any of the software support needed for this didn't make it into the OS (7.6/8) of the time, but may have been present in beta builds before the hardware was changed.

This should mean that whilst the standard functions work the additional chips and VCI slot on my prototype are unlikely to be supported fully in the classic Mac OS, and certainly not in OS X - which barely had support for the Beige G3 (and never did support the video options properly on these machines).

Will post again when the ROM SIMM arrives.

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Joined: Jun 1 2004
Posts: 67
ROM SIMM...

Slow but steady progress has been made with duplicating the ROM SIMM. Trag has asked me to confirm some of the layout pins on the ROM SIMM (which is actually a DIMM as the pins on both sides are different).

The details are:

I shipped him over some parts for the ROM DIMM, and he's also using some leftovers of his own to construct it.

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Joined: Dec 20 2003
Posts: 57
Re: PEX Revisited Part III

Just thought I'd post an update in case anyone is still reading...

I'm still working on the ROM DIMM. The original plan was for me to simply make a ROM DIMM with sockets for the chips. Then James could program his own chips as needed until he got something working.

Now this is tricky, as the PEX is in the UK and I'm in Texas and ordinarily there wouldn't be any way to test that the ROM DIMM worked.

However, the ROM DIMM (the circuit board, not the chip contents) for the PEX is the same as was used in the x100 (NuBus) through the Beige G3 machines. The X500 and X600 machines use the same ROM DIMM. In the Beige G3 the Vcc (power supply) pins are shifted to different pins. This is because the Beige G3 DIMM uses 3.3V and the earlier ones (and the PEX) use 5V. That way, if you stick a 5V DIMM in a 3.3V machine or vice versa, the DIMM just doesn't get any power. This may shed some light on the results several threads back when someone tried putting a Beige G3 ROM in their PEX.

Okay, so the PEX ROM DIMM is the same. I ran off about 200 circuit boards several years ago to use as Apple ROM DIMMs and I had a few boards left over. The idea was to put chip sockets on these boards.

James supplied the sockets (PSOP44 chips) and I did that. Then to test it (see three paragraphs back) I installed PM9600 ROM chips and tried it in a PM9600. And it didn't work.

After much gnashing of teeth and pulling of hair, I decided that I just can't get these sockets to work. Not too surprising as PSOP44 sockets are tricky. But darn it. They should work.

Then I went back and confirmed that I really did know how to build a 9600 ROM and that I was using the correct chips in the correct sockets, by soldering chips directly to the boards, which has always worked for me. So that was more months (at my glacial pace) of time.

So, where we are now, almost two years after James first contacted me (yes, I'm lame and slow, but *), is I plan to solder PEX programmed chips directly to the board and send it to James. The problems with that are 1) No way to test it after I build the thing, unless Mark Crutchfield still lives in Austin, TX? 2) We're not 100% that what James has dumped from the PEX using ROM dumping utilities is an accurate reflection of what's on the ROM DIMM.

* From paranthetical comment above:
..., but, in my defense, I had the original socketed DIMM built within six months of getting the sockets from James, which was also slow, but I told him I'd be slow. So that was reasonable. It's all the testing and writhing since then that has really eaten up the time. If all the excuse making sounds like I feel guilty, well, yes, that's very perceptive of you.

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Joined: Dec 20 2003
Posts: 256
Re: PEX Revisited Part III

Good to hear that some progress is being made. I would have hated to have this just fade away completely.

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Joined: Jun 16 2008
Posts: 5
Re: PEX Revisited Part III

well,

even without the ROM Simm wouldn't it be possible to:

-install 0SX (10.1 or 10.2) on a PCI PowerMac with XPF 4

-get the NVRAM settings from this mac, copy them..

-install the disk in the PEX

-apply these nvram boot args with right /dev etc to the PEX nvram

?

can't get no sleep...

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Joined: Jun 1 2004
Posts: 67
Re: PEX Revisited Part III

Hi,

This might be possible on more finished versions of the PEX (aka DigiBarn's) but the ROM SIMM seems to be needed on mine to get even a proper Open Firmware boot working.

I've tried a lot with the original PEX PLCC chips (and the updated ones that I've copied from the DigiBarn) but it really seems to need the ROM SIMM to actually boot.

However, I have not managed to get any version of OS X to boot from openfirmware under these 'ideal' conditions - so you're right this still might be a possibility without the rest of the ROM for booting OS X.

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Joined: Jun 16 2008
Posts: 5
Re: PEX Revisited Part III

Hi,

I saw that your PEX has now a ROM SIMM and boots fine to Classic OS, then it might be possible to run XPF 4 and install 10.2?

.. or OS X Server 1.2 aka Rhapsody (the system disk CP requires then MacOS 8.6)

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Joined: Nov 4 2005
Posts: 4
Re: PEX Revisited Part III

My return with a gem for all.

My name is Jeremy, some of you might know my by my former handle of TiMacLover, who frequented the 68kmla forum many moons ago.

I was clearing our an old storage unit of mine this past weekend, when I stumbled upon what I believe is a PEX motherboard, I acquired it some years ago through an eBay auction by a former Apple hardware engineer.

Please examine the following photos. It does not have the ROM stick Sad

I would like to sell the item to someone who will put it to good use and value it highly. I'm not looking to roll the bank and I am considering to place it on eBay.

http://i41.tinypic.com/257hfrr.jpg

http://i41.tinypic.com/2l8kbqd.jpg
http://i42.tinypic.com/xoecme.jpg
http://i41.tinypic.com/24b850x.jpg
http://i41.tinypic.com/59u9j.jpg

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Joined: Dec 20 2003
Posts: 57
Re: PEX Revisited Part III

truthstar wrote:

My return with a gem for all.

My name is Jeremy, some of you might know my by my former handle of TiMacLover, who frequented the 68kmla forum many moons ago.

I was clearing our an old storage unit of mine this past weekend, when I stumbled upon what I believe is a PEX motherboard, I acquired it some years ago through an eBay auction by a former Apple hardware engineer.

http://i41.tinypic.com/257hfrr.jpg

Probably way too late, but that is not a PEx logic board. It looks like a development board for the 7200. It is identical to the 7200, except that the ROM chips seem to be missing, and there are some DIP switches installed, where, I think, the 7200 has resistors. It would be interesting to know what those switches/resistors control...

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Joined: Dec 19 2003
Posts: 1687
Re: PEX Revisited Part III

trag wrote:

It would be interesting to know what those switches/resistors control...

My guess would be processor speed.

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