Re: COSMAC variants
On Mon, Sep 14, 2020 at 01:30 PM, Dennis Boone wrote:
It's my impression that the difference between the CDP1802ACE and theHi Dennis - That is what the data sheets say, but in 2017 I took some measurements comparing 9 genuine RCA CDP1802AEs, 6 genuine RCA CDP1802ACEs and 3 "seller refurbished" (marked Intersil) chips with similar underside numbers to make a 9:9 comparison. I posted the results to the group in a thread that can be found by searching the group messages with the string "challenge 1802ae". Herb Johnson has a created a page on his website that summarizes my results here http://www.retrotechnology.com/memship/1802ACT_tests.html . [Note that the youtube videos aren't there anymore.]
There are links on that page where Herb has collated my posts and those of other group members. They are here:
In summary, while it would seem reasonable to assume that an ACE could be an AE chip that failed testing, I found no significant differences between the different versions when VCC=VDD from 5V to 15V and VCC=5V and VDD 5V to 12V.
Running VCC (the I/O voltage supply) higher than 5V isn't worthwhile due to the difficulty of up shifting from 5V to VCC for 5V only parts like EPROMs, the time delay through the level shifting devices was longer than a clock cycle at the frequencies I had already reached using VCC=5V and VDD=5-12V. Devices marked "MALAY" or "SINGAPORE" on the bottom (which I'm reasonably certain weren't made by RCA, but Harris or Intersil) seem to be a faster chip design.
I'd suggest that any used or "seller refurbished" 1802 has been running for way longer than the burn in period for "X" devices so I doubt you'll notice any difference. So in summary, I suspect the following, "C" devices have been tested to the "C" specifications. The may also have been able to pass the non "C" specifications but weren't tested for those, so as your wrote "spec-limited to 6.5 V" for "C" versions not actual device limitations to 6.5V.