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41CL Strange Behavior??
07-26-2021, 04:10 PM
Post: #1
41CL Strange Behavior??
Hi all,

I reset my 41CL today (aka Memory Loss). I disabled the MMU (MMUDIS), and cleared it as well (MMUCLR).
This is when I noticed a very strange behavior. I don’t know if it’s normal, but, to me, it doesn’t seem to be.
Here is what I noticed:

When the MMU is disabled and nothing is plugged in to the calc, a CAT 2 responds perfectly. Same thing with a Card Reader plugged in —> Cat 2 is fine.

Now, when an HP-IL is plugged in (still with MMU disabled), CAT 2 returns a nasty and blurry “DATA ERROR”. See attached picture. At that point the HP41 freezes, and I have to remove to battery pack (not batteries, the rechargeable pack) to turn it off and reset it.

On the other hand, when the MMU is enabled (even with nothing virtually plugged in), everything works perfectly as they should. I mean that it works with no error just by enabling the MMU after a hard reset. This weird behavior doesn’t happen with a Card Reader plugged in. Just the HP-IL unit.

The unit works fine when the MMU is enabled, and it also works fine with my other 41CX unmodified machine. It also works perfectly with the PIL-BOX.

Is this normal?? Should I be worried?
If it’s not normal, how do I fix this issue?

Regards


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07-26-2021, 06:43 PM (This post was last modified: 07-26-2021 06:48 PM by Sylvain Cote.)
Post: #2
RE: 41CL Strange Behavior??
(07-26-2021 04:10 PM)Neve Wrote:  Is this normal?? Should I be worried?
Yes and no.

(07-26-2021 04:10 PM)Neve Wrote:  If it’s not normal, how do I fix this issue?
You cannot.

When Monte created the 41CL 10+ years ago he did not know at the time the HEPAX method of dynamically moving its ROM around,
so he statically assigned its 41CL Extra Functions (YFNZ) ROM to page 7 and in so creating a conflict with the HP-IL module.
This is explained in the 41CL User Manual at page 18.
Because it is part of the core system, it cannot be updated with a normal ROM update and we all have to live with it.

Rule #41: always remove the HP-IL module before disabling the MMU. Wink

Sylvain

Edit:
(07-26-2021 04:10 PM)Neve Wrote:  The unit works fine when the MMU is enabled, and it also works fine with my other 41CX unmodified machine. It also works perfectly with the PIL-BOX.
It is because you have mapped the YFNZ or the YFNX ROM to another page and you left the page 7 free in your MMU configuration.
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07-26-2021, 10:10 PM
Post: #3
RE: 41CL Strange Behavior??
(07-26-2021 06:43 PM)Sylvain Cote Wrote:  
(07-26-2021 04:10 PM)Neve Wrote:  Is this normal?? Should I be worried?
Yes and no.

That’s a relief. Thanks.

(07-26-2021 06:43 PM)Sylvain Cote Wrote:  When Monte created the 41CL 10+ years ago he did not know at the time the HEPAX method of dynamically moving its ROM around,
so he statically assigned its 41CL Extra Functions (YFNZ) ROM to page 7 and in so creating a conflict with the HP-IL module.
This is explained in the 41CL User Manual at page 18.
Because it is part of the core system, it cannot be updated with a normal ROM update and we all have to live with it.
Ok, I get it.
(07-26-2021 06:43 PM)Sylvain Cote Wrote:  Rule #41: always remove the HP-IL module before disabling the MMU. Wink

Sylvain
. I’m not sure I always did, but I will from now on.

(07-26-2021 06:43 PM)Sylvain Cote Wrote:  Edit:
(07-26-2021 04:10 PM)Neve Wrote:  The unit works fine when the MMU is enabled, and it also works fine with my other 41CX unmodified machine. It also works perfectly with the PIL-BOX.
(07-26-2021 06:43 PM)Sylvain Cote Wrote:  It is because you have mapped the YFNZ or the YFNX ROM to another page and you left the page 7 free in your MMU configuration.

Even without mapping the YFNX ROM to PLUG1L? Just by enabling the MMU? Hmmm…

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07-26-2021, 10:35 PM
Post: #4
RE: 41CL Strange Behavior??
(07-26-2021 10:10 PM)Neve Wrote:  Even without mapping the YFNX ROM to PLUG1L? Just by enabling the MMU? Hmmm…

Yes. If the MMU is disabled YFNZ is mapped to page 7 by hardware outside of the MMU. If the MMU is enabled this special hardware is disabled and only the MMU programming applies.
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07-26-2021, 11:27 PM
Post: #5
RE: 41CL Strange Behavior??
(07-26-2021 10:35 PM)Monte Dalrymple Wrote:  
(07-26-2021 10:10 PM)Neve Wrote:  Even without mapping the YFNX ROM to PLUG1L? Just by enabling the MMU? Hmmm…

Yes. If the MMU is disabled YFNZ is mapped to page 7 by hardware outside of the MMU. If the MMU is enabled this special hardware is disabled and only the MMU programming applies.

OK, thanks Monte. I guess all is good then. To be honest, I was a little scared.

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