The RCA 1802 microprocessor was originally prototyped using TTL !

The RCA 1802 was (I *think*) the original CMOS microprocessor chip.  But I was surprised to learn that the design was prototyped using TTL logic (196 chips!):

http://www.cosmacelf.com/publications/books/system-00-manual-orig.pdf

Why was this a surprise ?  Because RCA was the originator of the 4000 series of CMOS logic chips, I would have bet money that the breadboard version of the 1802 processor would have used 4000 series CMOS but NOPE.

On the 4th page of the document it mentions that the unit uses 100 watts of power, 60 of which are for the display !  

The document was dated 1971, the circuitry was eventually converted to CMOS and put onto a single chip.  That 1802 chip was used in home computers:

The COSMAC ELF home computer used the RCA 1802 microprocessor

but found a very important niche in aerospace applications, many by NASA.  The CMOS process could be adapted to SOS (Silicon on Sapphire) which rendered it immune to the problem of latch-up which was a bugaboo with early CMOS processes.  In addition CMOS had fewer problems with noise and also was much lower power than something like TTL.  The processor was a static design so it could be stopped or the clock run at low frequencies to further decrease power usage.

I remember going to the 1979 IEEE Cherry Hill test conference and seeing a presentation by a fellow who consulted for NASA.  He had built a hardware fault simulator for the RCA 1802 where each node of the circuit could be stuck high or low.  Then an IC tester would be used to see if the fault could be detected.  This concept was patented (US4308616): 

https://patents.google.com/patent/US4308616A/en    

Here is a paper on the 1802 hardware fault simulator results: 

https://ntrs.nasa.gov/api/citations/19800012553/downloads/19800012553.pdf

I don't know if NASA ever extended this hardware simulation to more complicated microprocessors.  I do remember the presenter's ending punch line when asked why 100% fault coverage was desirable he replied something like:  "our customer returns come in the form of fireballs".  In other words, NASA has to get things right or the whole thing can go blooey !

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm