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Topic: How microprocessors work (Read 2 times) previous topic - next topic

Nick Gammon

There is a very interesting talk here:

http://www.youtube.com/watch?v=K5miMbqYB4E

This fellow (Michael Steil) talks about how they reverse-engineered the 6502 chip.

Amongst other things he shows this page, which is the control logic for the chip:

http://www.weihenstephan.org/~michaste/pagetable/6502/6502.jpg

They etched the top off the chip off with acid, started taking photos, removed more layers, took more photos, and gradually built up the exact way that all the transistors (MOSFETs) were connected together.

Example of the layers: http://blog.visual6502.org/2010/11/6502-layer-images.html

Then they made a hardware simulator that shows the exact logic lines that are asserted, for each clock cycle, of each instruction.

There is a simulator you can play with on your web browser: http://visual6502.org/JSSim/index.html

Jack Christensen

I just had a quick look, it is certainly all very cool, but why do it? Surely the masks and other doc are preserved in some form? 6502s can still be purchased, I assumed they were still being produced, or are they NOS? That was a long time ago!

I like the visual simulator. Reminds me a bit of a demo I once saw of a TTL chip in an electron microscope. The state of the various areas was visible as the electrons were attracted more or less depending on whether the area was high or low.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

Nick Gammon

Quote

Surely the masks and other doc are preserved in some form?


Apparently not, or at least, not the documentation. Maybe they have the low-level dies to make the chips from, but it sounds like no-one knows why the transistors are laid out that way. The company has changed hands multiple times, it seems.

For me it's interesting to see how (at least in part) the processor chip "works". I've often wondered what exactly happens at the chip level when it "executes" an instruction, and those talks make things a bit clearer.

rockwallaby

That is very cool Nick.
Brings back memories, though I was one for Motorola 68XX, 68HCXX and before that those very sexy Zilog's.
So I went straight to find a Zilog image, not a plain jane Z80 which I knew intimately, but they have a Z84C00.
Image is here http://visual6502.org/images/Z84C00/Z84C00_die_shot_20x_1b_1600w.jpg

I wonder if they have a signetics 2650 in their files?

_____
Paul

Osgeld


I just had a quick look, it is certainly all very cool, but why do it? Surely the masks and other doc are preserved in some form? 6502s can still be purchased, I assumed they were still being produced, or are they NOS? That was a long time ago!

I like the visual simulator. Reminds me a bit of a demo I once saw of a TTL chip in an electron microscope. The state of the various areas was visible as the electrons were attracted more or less depending on whether the area was high or low.


Western Design owns and produces the 65c02 as of now, and its still a hot seller as simple deeply embedded cores that SOC's are made around

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