Bus Pinout on Proto #3

[Scott Robison]

10 minutes ago, BruceMcF said:

It didn't modify the operation of their existing design except for the $x7 and $xF opcodes no longer being NOPs, and Rockwell sold theirs as 65C02's (maybe R65C02?), so it likely made sense in selling the updated chips as a second source to the target company. They weren't selling the two versions side by side, after all ... the 6502's at that time were selling briskly enough for industrial control boards that a month of overlapping inventories for a fully backwards compatible upgrade wasn't a problem.



Also IIRC (so no guarantees), the 65CS02 was not about the change in instruction set, it was about revising the chip to be fully static ... though at the same time additional instructions were added. The Rockwell and Western Design versions were fully static from the outset, so they had no need to single out their fully static version.



One thing I certainly don't recall is whether MOS or Fairchild or somebody else took the lead in the CMOS version of the CPU.

My understanding is the WDC was the lead on CMOS 6502.

65C02S is the fully static current part, but that is not the same as 65SC02. It really doesn't matter, I guess. I'd just like to know the real history and rationale for 65SC02 (because I guess the S position is important).

[Scott Robison]

According to http://forum.6502.org/viewtopic.php?f=4&t=1383&sid=4442153f5d07a1b0c9a9b4803b0cbd59&start=15 (which I guess is going to have to satisfy my curiosity):



Original 65C02 from WDC did not have bit instructions. Rockwell added them and WDC copied them (presumably for the second source reason @BruceMcF gave above).

GTE apparently used 65SC02 in their part numbers of the original 65C02 IP. Presumably once 65C02 (originally with a B suffix, now no suffix) had the bit instructions I'm going to assume WDC added the 65SC02 to their line to "second source" the GTE so there was identical parts available for both third party products. They've since dropped the 65SC02.

[BruceMcF]

On 7/16/2021 at 5:50 AM, Scott Robison said:

My understanding is the WDC was the lead on CMOS 6502.



65C02S is the fully static current part, but that is not the same as 65SC02. It really doesn't matter, I guess. I'd just like to know the real history and rationale for 65SC02 (because I guess the S position is important).

No, that's right, the fully static part is suffix S. Rockwell licensed the earlier "half-static" version from WDC, which could hold clock high indefinitely, but not clock low. Since Rockwell licensed Western's design, it seems likely that "their" bit instructions was something they hired Western to do, to streamline their modem code, which would explain why Western was the company able to second source Rockwell's version. And since Western's version was fully static, the second source was an upgrade on the original source.

[BruceMcF]

It bears keeping in mind that it's not unusual for standard government contracts to give preference to parts that are available from more than one supplier, so it is possible that a different provider as a second source of a compatible part can be a useful step to land a large government order. In that case, rather, "hey, why are you selling the customized design I ordered from you?" it can be, "c'mon, how soon am I going to be able to show that you are also selling the customized design I ordered from you?"