Date: Tue, 30 Sep 2003 06:45:00 -0500 From: Derek Morton <[EMAIL PROTECTED]>
You could always remove the GALs and try to extract the program...
I have a Needham EMP-30 programmer <http://www.needhams.com/e30.html> but have not programmed or read any PLDs. Is reading the program in a PLD a normal/common function for a universal chip programmer? I may need to get the PLCC adapter...
If they were not protected you will be fine (just don't overheat the devices or you will ruin the program).
Overheating is something I have been wondering about. Are PLDs more heat sensitive than other chips? I'm good at soldering and desoldering. I've taken 208 pin PQFPs off of boards and moved them to others (Hammerhead, Bandit on the PMac x500 series) without damaging the chips.
However, I desoldered a couple of GAL16V8's off of the accessories to my Outbound Laptop 125 (SCSI adapter, external floppy controller) and I think I burned them. This was before I had a programmer of my own. I sent them to a fellow I found on comp.sys.ibm.pc.hardware.chips (well there isn't an analogous Mac group) to have them read and he couldn't get a thing off of them. When he returned them and I tried reinstalling them (I had put in sockets in the meantime) on power up, they don't function and the chips grow quite warm.
My goal was to build some copies of the SCSI adapter and the external floppy for the Outbound Laptop. I've obtained two more of each accessory, despite their rarity. But I'm frightened to attempt removing the GALs for fear that touching them with the soldering pencil will clear/destroy them.
At this point, I'm afraid to take a soldering pencil near any PLD, until I get more information. Do you have any experience desoldering PLDs?
Am I correct in believing that even if the PLD is protected, if it was programmed only in combinational mode it's not too hard to determine the programming. It's when the thing is a state machine, that it becomes difficult or impossibly complex.
The GALs themselves are standard 16v8 / 20v10 parts (if memory serves), but the speed will likely be a problem if you try running it at 160% of it's rated speed (much like the SRAM). I have both a 25 MHz and one or two 33 MHz cache cards, but where there are in my piles-o-stuff is another question, if I can (easily) find them I will let you know the speed ratings of the devices.
I compared my 25 MHz Quadra cache with the cache module for the Daystar Turbo040. They're built with similar SRAM and tag RAM chips, and both use four PLDs. However, the Turbo040 cache, which is built to go to 40 MHz uses faster parts in all three categories. So I suspect that you are correct, and even if I change the SRAM and tag RAM, the PLDs still won't keep up.
GALs are a very bad thing for us vintage Mac users. People worry about eventually not being able to get power supplies or pictures tubes, when they should also be concerned about what is going to happen when the program in their computers GALs degrades to the point of corruption. Modern devices have a fairly long program life, but some of the older chips were only guaranteed for around 20 years (although hopefully they will last much longer than that).
It would be quite a job to go around and remove samples of all the GALs and read and store their contents. Especially if protecting them was common practice.
Realize that the performance boost from this type of cache card is minimal. Since there is no true cache controller in the system (unlike the 68030), these cache cards are (I believe) single segment, fixed memory space write-through caches which probably sit at the bottom of the system memory and help most with system calls.
It might not be worth the effort then. I just figured I'd have something to put in that PDS slot. I'm not interested in a PPC upgrade, as these days, if I want a PPC, it's much cheaper and convenient to just get an x100 machine. Daystar did an amazing job of engineering its upgrades, but they still come with a bunch of compatibility details one must track to use them efffectively with things like the JackHammer card and later OSs.
Thanks for all the information. I hope I have not overwhelmed you with additional questions. My biggest wonder at this point is about the practicality of desoldering PLDs without damaging them.
Jeff Walther
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