Re: BRK opcode

From: Brian Ketterling (
Date: 2003-11-07 01:20:02

>From: Anders Carlsson <>
>How does the 6800 do BRK (if it has a similar op-code at all)?...

I dunno.

>...I don't
>know to what extent the story about Motorola technicians jumping off
>the boat and forming MOS is true, but the 6502 does have some traits
>from the 6800?

I think there's a document on some C= site that straightens out and details 
the whole story, but in general it's true.  If I recall correctly, the gist 
of it is that while working at Motorola, they wanted to "do" a PDP-8 on a 
chip, which became the 6800.  In the meantime, the PDP-11 had come out.  
They worked on a microprocessor version of that, but Motorola wasn't 
interested in developing it (we've got ONE microprocessor -- how many do you 
need?), so they left and started MOS.  Their "PDP-11" work became the 6501, 
but because they'd worked on it at Motorola, the company considered it their 
intellectual property and sent their lawyers after MOS.  MOS agreed not to 
market the 6501, and developed a variation, the 6502.  -- Apologies for any 
details I've screwed up (it's been some time since I read about this), but I 
think that's pretty much the story, and in fact the 6800 and 6502 were done 
by the same people.  Presumably they didn't entirely scrap their earlier 
work, and carried a lot of the design over to the 6502.

The same thing also happened at Intel: some 8088 engineers left to start 
Zilog so they could pursue their own better idea, the Z-80.

-- Brian

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