Re: R6502AP

From: Nate Lawson <>
Date: Sat, 29 Nov 2014 12:44:02 -0800
Message-Id: <>
On Nov 26, 2014, at 4:18 PM, wrote:

> On Thursday 27 November 2014, 01:08:43 wrote:
>> On 2014-11-27 00:54, wrote:
>>> On Thursday 27 November 2014, 00:46:29 wrote:
>>>> Should I expect any troubles after replacing MOS6502s with R6502APs?
>>>> Undocumented opcodes' incompatibilities? Other gotchas?
>>> rockwell and synertek licensed the 6502 from MOS, so these should be
>>> identical to theirs...
>> That would mean that they licenced down to the mask level. Was this the
>> case? Or just rights to make own design based on the MOS one. If that's
>> the same design then it should be compatible even with all undocumented
>> opcodes.
> as far as i know they licensed the mask (not only for the 6502, but also for 
> other chips)

The only thing they could license at the time was the mask. The 6502 wasn’t created via CAD software, but by hand-drawing lines. They had packed the 6502 mask pretty carefully, so I think there wasn’t room to do much rework.

By the CMOS days, I assume Rockwell or Commodore copied the original design into CAD, which made it easier to fix bugs and add features. They’d have to redraw it from scratch anyway since the gates would all be from a different process.


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Received on 2014-11-29 21:00:40

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