Re: And the 25c only saved LASTX Message #3 Posted by Vieira, Luiz C. (Brazil) on 14 May 2003, 4:08 p.m., in response to message #2 by Gene
Hi;
after Katie's wise words and your observation, I add the fact that the ACT chip, if containing stack registers, may not contain the LASTx. Both HP21 and HP37E have no LASTx access, maybe no LASTx register too. Are there others without LASTx?
Then we conclude (hopefully in a correct reasoning) that the LASTx register is in fact in RAM, not in the ACT chip, what explains the fact it is kept in the HP25. As it is not so practical, maybe a remanagement in the HP19C/29C exchanged their places. I agree with Katie but I believe that as RAM was an expensive resource at that time, they have simply used LASTx holding feature and rearranged addresses so users would take the advantage of having at least the X-register back.
Wrong reasoning? Maybe. This would not need a new internal ACT design, just new ROM coding with the X-register addressed in RAM and LASTx addressed inside ACT.
My 2¢ (now I know how to get it...)
Luiz C. Vieira - Brazil
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