More Fun With Apple’s Internal Tools: Creating A PDS Card #Apple #ReverseEngineering @dt_db

Republished By Plato

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Doug Brown recently figured out how to use Apple’s leaked Flasher utility from the 1990s to reflash a ROM SIMM inside of a Performa 630. It’s basically the Mac equivalent of a BIOS update, but only for Apple’s developers.

The research involved in that post was quite a journey of reverse engineering from both a software and hardware perspective. But what was PDS ROM Info?

I had to disassemble the code to figure out which computers were compatible and what the software was expecting to find. I also had to create a replica of an Apple development ROM SIMM that was wired exactly the way Macs of the era expected it. Although I was very excited about my discoveries, one big question remained:

What was the purpose of the bottom right half of the main window labeled “PDS ROM Info”? And what would it take to enable it?

PDS stands for Processor Direct Slot. It’s an expansion slot that provides most of the CPU’s signals and can be used for adding things like Ethernet, a video card, or an accelerator. If you look at the comments on my last post, you will see some discussion about the PDS cards used by the Flasher app (thanks Al!). It sounds like they were used to flash programmable ROM SIMMs/DIMMs, and there were multiple generations of cards. That makes sense, because the list of compatible models covers a variety of systems with different PDS slots. Some of the Quadra machines like the 700, 900, 650, and 800 have a 140-pin 68040 PDS slot. The LC 475, 575, 580, and 630 have the 96-pin LC PDS slot that came from the original Mac LC, with an extra set of 18 pins that can optionally be used by fancier cards. The 610 has a card slot that takes an adapter board to give you either a NuBus slot or 140-pin PDS slot.

Even though I still have no idea what Apple’s original PDS cards used by developers looked like, I really wanted to rig something up to get the PDS portion of this software working. So I went to work disassembling the Flasher utility and researching classic Mac hardware and Motorola MC680x0 processors.

See how Doug goes about figuring it out and using period hardware to test it in the post here.