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A 'once and for all' declaration regarding L88M mask MC68040 CPUs


Well-known member
I've searched a few threads and wanted to make a place for a 'once-and-for-all' declarative thread regarding these final incarnations of the MC68040 CPU.
I've read many things and heard many testimonials, but I wanted to definitively understand what people mean.

Most of the time, this is what I see written about them:
they run cool to the touch
Which I take to mean, "these can run without a heatsink" and also "there's little perceptible temperature differential when 'touched'"

Is this truly their behavior, globally? Were they meant to run like this, or are the takes like this simply the anecdotes from various users? I'm not looking to cast blame, I just want there to be more of an empirical reference point for these, because, you hear things and things get passed around.

And if this (above) is taken to be true, is it enough to declare CPUs that are marked such, but do not run this way as 'fakes' or 'counterfeits?' AND MORE TO THAT POINT: what is an unacceptable range of temperature operation?

I have some E42K mask versions that would probably run ~50–60C at stock speeds without a heatsink, but would be interested to know the range in the real world. Modern CPUs operate around that at load or higher, even. I've seen in the Freescale documentation something close to 101C being the upper limit, but I don't recall for certain. Obviously, we don't want to run in that range, but within an acceptable one.

Ideally, I would appreciate the insight of anyone who worked at a Motorola fab during the period, but on the other hand I'd also understand if any such person would prefer to keep quiet on the matter .
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Well-known member

I have a bunch of 68040s from various systems and a couple bought off eBay as well as a Flir thermal imaging camera for my iPhone. I'm thinking about setting up some sort of test bed (perhaps my Quadra 605) and swapping in all the 68040s CPUs I have (including "suspect" L88M and E42K eBay CPUs)

E31F - .8um masks:
Have 1 E31F @ XC68040HRC25 - In C650 25MHz
Have 1 E31F @ XC68040RC33M - In Q630 33MHz
Have 1 E31F @ XC68040RC25M - In Q610 25 MHz

E23G - .65um masks (not sure about this mask/die shrink?)
Have 2 E23G @ XC68LC040RC25 - In Q605 25 MHz
Have 1 E23G @ XC68LC040RC33B - In LC580 MB 33MHz

E42K - .65um masks
Have 1 E42K @ MC68040RC33 - from eBay

L88M - .57um masks
Have 1 L88M @ MC68040RC33 - from eBay

My gut (which admittedly doesn't have a perfect track record) has a hard time believing L88M CPUs are actually "cool to the touch" when in active operation, cooler than early mask versions yes but cool...? Of course without a known legitimate L88M I'm not sure what I could prove.


Well-known member
not sure about this mask/die shrink?
This is from the German AmigaWiki, (and until it's corrected in the same manner I'm hoping for the rest of it, it's the best we have), and they mention that full 040s had different masks from the LC and EC versions. Here are the full version masks from that wiki:

D43B 1989 0.8µm XC
D50D 1989 0.8µm XC
D98D 1989 0.8µm XC
E31F 1989 0.8µm XC
E26A 1992-19950.65µm XC
E42K 1995 0.65µm MC
K63H 2000 0.57µm MC
L88M 2002 0.57µm MC