HP25c continous memory

[isanchez]

Dear all,

I was playing with my HP25c and some doubts came to me:

I realised that the continous memory does not involve the stack, only to the registers and programming isssues, am I right?

On the other side, I reviewed all HP25 manuals I have (paper and digital), to check this and I did not find any mention to the HP25c specs. Maybe they were old editions? Is there any specific manual for HP25c?

Thanks and kind regards

Ignacio

[Steve Simpkin]

(02-16-2021 11:50 AM)isanchez Wrote:  Dear all,

I was playing with my HP25c and some doubts came to me:

I realised that the continous memory does not involve the stack, only to the registers and programming isssues, am I right?

On the other side, I reviewed all HP25 manuals I have (paper and digital), to check this and I did not find any mention to the HP25c specs. Maybe they were old editions? Is there any specific manual for HP25c?

Thanks and kind regards

Ignacio

The HP-25C included an additional 16 page pamphlet called Getting The Most From Continuous Memory that explained what was saved in Continuous Memory and how to best use it. The following was saved when the HP-25C was turned off: all 49 program steps in program memory, all 8 data storage registers and the Last X register. As you know, the stack was not preserved.
Here is a copy of the pamphlet.
https://literature.hpcalc.org/community/hp25c-cm-en.pdf

[CY-CL]

Hi Ignacio

You can change the ACT Chip trough a PANAMATIK Chip. Then you have an overall continuous memory. You can install a socket; in this case you can swap back to the original ACT anytime.

Patrik


ACT Chip

[Didier Lachieze]

(02-16-2021 11:50 AM)isanchez Wrote:  I realised that the continous memory does not involve the stack, only to the registers and programming isssues, am I right?

Yes, for reasons explained here, in the 25C the stack registers are stored with the display format in the volatile ACT memory, not in the non-volatile memory chips where you have the program steps and LastX register. So the stack registers and the display format are not preserved during power off.

[Dave Britten]

(02-16-2021 12:12 PM)Steve Simpkin Wrote:  The HP-25C included an additional 16 page pamphlet called Getting The Most From Continuous Memory that explained what was saved in Continuous Memory and how to best use it. The following was saved when the HP-25C was turned off: all 49 program steps in program memory, all 8 data storage registers and the Last X register. As you know, the stack was not preserved.
Here is a copy of the pamphlet.
https://literature.hpcalc.org/community/hp25c-cm-en.pdf

Interesting, apparently I hadn't read that in very close detail before, as I didn't realize the 25C didn't detect power loss and start up with "Pr Error" like other models. It makes sense that they didn't have room to add error detection though, since the 25 ROM was pretty much packed full right to the last byte. What differences are there in the 25C ROM? Just the omission of the startup sequence that zeros out the registers and fills program memory with GTO 00?

EDIT: I read the linked response from PANAMATIK, and that's basically the gist of it, but the ROM is identical, and HP instead changed the new CMOS memory chip to ignore the "clear all memory" instruction sent from the ACT. Clever.

[isanchez]

Hi,

thanks a lot for all your comments!!
I was not aware of the pamphlet, it is very interesting!!
I already have the ACT chip of Panamatik, in fact I have a couple. In this case, I prefer to preserve the HP25c as is, in perfect working condition.

Yes, I realised also that the display format is not preserved.

Again: thanks a lot and kind regards

Ignacio

[teenix]

(02-16-2021 02:51 PM)Dave Britten Wrote:  Interesting, apparently I hadn't read that in very close detail before, as I didn't realize the 25C didn't detect power loss and start up with "Pr Error" like other models. It makes sense that they didn't have room to add error detection though, since the 25 ROM was pretty much packed full right to the last byte. What differences are there in the 25C ROM? Just the omission of the startup sequence that zeros out the registers and fills program memory with GTO 00?

No spare RAM either which is how the others detect a battery out reset, by storing a special value in RAM. For the 33C, the display information for "Pr Error", the 34C stores "EAE"

This is tested on power up, and if it is not there, as when batteries have been removed for more than that allowed, then the software does a full reset and clears all RAM registers and writes the special value to RAM.

In the case of the 33C, I'm not quite sure of the mechanism, as there is only supposed to be 16 RAM registers as far as I know, but this value is stored in RAM address 20. Maybe it is a special register in the processor chip so that normal RAM has full user functionality.

cheers

Tony