It's tricky to find the particular points of interest in such a long conversation, but here are a couple of pointers:
About using Moto's customers to help define the subset of the 6800 instructions which would allow for a cheap microprocessor:
https://youtu.be/wiv9417eYoY?t=1h7m54sAbout the Moto lawsuit:
https://www.youtube.com/watch?v=wiv9417 ... t=1h22m47s6502 for control - not for big software projects - and also about the strict die size target and the Special Bus, and the PLA (ROM) being 20 lines too wide:
https://www.youtube.com/watch?v=wiv9417 ... t=1h35m35sThe story as told here says the datapath was already done and was not changed at that point.
However, there's a hint in the layout of the datapath drivers that there were changes to the layout at some point, which has been taken to be evidence that the datapath used to be wider and perhaps had extra function. Specifically, the floating rectangle of diffusion (north east of the ALU out here
http://www.visual6502.org/JSSim/expert. ... &zoom=12.0) which looks like a point where one or more control line drivers were hacked out to reduce the X size of the chip.
In this thread
viewtopic.php?f=1&t=2015there's a quote from Chuck Peddle to the effect that they knew the extra die size cost of pushing A on interrupts, and couldn't afford it. It seems plausible that they knew the cost because they'd implemented it, and then had to remove it.
Elsewhere, Segher has opined that the 6502 originally had two accumulators, and that there are indications for this in the instruction encoding (and decoding), but that they were dropped for the same reasons of chip size.
Quote:
My strong suspicion is that originally the 6500 had *two* accumulators, and the instructions with low bits 11 were like those that now have 01, but for reg B instead of reg A.
It looks like "B" was removed when making the die less wide; mostly it saves a whole lot of PLA lines (the register itself takes almost no space). That's also probably why LDX # etc. are jumbled around: it takes less PLA space to decode this way.
You can easily see where PLA lines were removed: originally there was a ground divider every twenty (iirc) lines. More to the left the blocks have more lines missing now, which tells you what features were removed (or altered, simplified, etc.)
Edit: see also the discussion
over here.