Bigger ALPHA register

Discussion around the Swiss Micros DM42 calculator.
Thomas Okken
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Re: Bigger ALPHA register

Post by Thomas Okken » Thu Sep 20, 2018 12:17 pm

eulerfan wrote:
Thu Sep 20, 2018 3:00 am
Thomas Okken wrote:
Thu Sep 20, 2018 12:47 am
Programmable HP calculators have done that at least since the HP-25!
I actually owned an HP-25 and never noticed the feature. :lol:
That's really weird! :shock:

I dug a bit and that feature was, in fact, first introduced in the HP-25:
One innovative feature of the HP-25 is the behavior of the SST (Single Step) key in run mode. This key was designed to help the user debug programs. It allows the user to execute his program one key phrase at a time. When the SST key is held down, the display shows the line number and the key phrase that is to be executed next. Releasing the SST key executes just that key phrase, and the numerical results appear in the display. This new feature makes debugging programs quite easy because the user can tiptoe through his programs, seeing both the key phrases and their results, one phrase at a time. The display when the SST key is held down includes the step number, so checking program flow and branching is easy.
http://www.hpl.hp.com/hpjournal/pdfs/Is ... 975-11.pdf (page 5)

eulerfan
Posts: 6
Joined: Fri Aug 24, 2018 10:19 pm

Re: Bigger ALPHA register

Post by eulerfan » Thu Sep 20, 2018 2:38 pm

Thomas Okken wrote:
Thu Sep 20, 2018 12:17 pm
eulerfan wrote:
Thu Sep 20, 2018 3:00 am
Thomas Okken wrote:
Thu Sep 20, 2018 12:47 am
Programmable HP calculators have done that at least since the HP-25!
I actually owned an HP-25 and never noticed the feature. :lol:
That's really weird! :shock:

I dug a bit and that feature was, in fact, first introduced in the HP-25:
One innovative feature of the HP-25 is the behavior of the SST (Single Step) key in run mode. This key was designed to help the user debug programs. It allows the user to execute his program one key phrase at a time. When the SST key is held down, the display shows the line number and the key phrase that is to be executed next. Releasing the SST key executes just that key phrase, and the numerical results appear in the display. This new feature makes debugging programs quite easy because the user can tiptoe through his programs, seeing both the key phrases and their results, one phrase at a time. The display when the SST key is held down includes the step number, so checking program flow and branching is easy.
http://www.hpl.hp.com/hpjournal/pdfs/Is ... 975-11.pdf (page 5)
Yeah, weird, I really liked that old -25 and used it a lot. It had such a small program memory though that I hardly ever used the SST key.

Thomas Okken
Posts: 492
Joined: Tue May 02, 2017 3:48 pm
Location: New Jersey, USA
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Re: Bigger ALPHA register

Post by Thomas Okken » Thu Sep 20, 2018 7:27 pm

eulerfan wrote:
Thu Sep 20, 2018 2:38 pm
I really liked that old -25 and used it a lot. It had such a small program memory though that I hardly ever used the SST key.
Yeah, that program memory was so small that after a while I knew several of the more useful programs by heart (the root finder and moon rocket lander come to mind). I did manage to write a couple of tricky programs on it, though, like an any-to-any base converter. Without the HP-25 SST behavior, those would have been a nightmare to debug!

eulerfan
Posts: 6
Joined: Fri Aug 24, 2018 10:19 pm

Re: Bigger ALPHA register

Post by eulerfan » Fri Sep 21, 2018 9:47 am

Thomas Okken wrote:
Thu Sep 20, 2018 7:27 pm
Yeah, that program memory was so small that after a while I knew several of the more useful programs by heart (the root finder and moon rocket lander come to mind).
I never tried to memorize any programs; it was usually easier to write them as needed. One thing I disliked about the -25 was that my program disappeared whenever I turned the calculator off, so I kept the code short.
I did manage to write a couple of tricky programs on it, though, like an any-to-any base converter. Without the HP-25 SST behavior, those would have been a nightmare to debug!
My usual debugging technique was to place R/S instructions at key locations. The calculator would stop executing the program when it reached one of those spots, and then I could look around. Another thing I remember disliking about the -25: there was no way to insert an instruction, so I would often have to use a "patch": a GTO to some unused spot, where I would place the R/S, the instruction that the original GTO overwrote, and a GTO back to the program. All this was still quicker than using SST a lot.

This really brings back memories. :D My HP-25's keyboard wore out, but I think I still have the "HP-25 Applications Programs" handbook -- lots of good stuff in there.

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