HP-25C Eumulator

[Thomas Okken]

(04-20-2017 07:02 PM)PANAMATIK Wrote:  The transition from HP-25 to HP-25C by HP was ingenious and made a very fast time to market possible at these competitive days. The firmware remained bit by bit identical, even the "Clear Memory" instruction, which cleared the external RAM chips at initialization, was left in place. There were only two hardware changes made: the two NMOS RAM chips were replaced by two pin compatible CMOS RAMs, and battery plus was connected to a previously unused pin of these RAMs. As the NMOS RAM chips itself (and not the ACT processor) decoded and performed the "Clear Memory" instruction, the CMOS RAMs decode unit was modified and just didn't execute this instruction.

But then how did the RAMs get cleared on cold start?