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cdmackay · 03-04-2020, 12:47 AM

I've noticed that every time I update my 41CL, the MMU gets disabled when I disconnect the serial cable.

I'm careful to never connect or disconnect the 41CL end whilst the PC end is powered. i.e. when connecting I connect the 41CL end first, and when disconnecting I disconnect the PC end first.

Connecting the cable (at both ends) does not disable the MMU, but when I disconnect the PC end (first), the 41CL MMU gets disabled.

This can't be an artefact of the serial jack at the 41CL, since the MMU gets disabled at soon as I disconnect the PC end, even with the 41CL serial jack still in.

If it makes a difference, I use a Prolific USB-serial cable at the PC end (actually a Mac laptop).

Obviously, this is not a big deal, since XEQ MMUEN always brings things back. But is this expected?

Finally, on a vaguely related note, I note that Ángel Martin's excellent PWRX PowerCL Extreme module has a key shortcut for MMUEN (ΣCL M E). But if the MMU is disabled, you lose access to your plugged modules, so you won't be able to use it, surely?

Sylvain Cote · 03-04-2020, 02:08 AM

(03-04-2020 12:47 AM)cdmackay Wrote: I've noticed that every time I update my 41CL, the MMU gets disabled when I disconnect the serial cable.

I do not know if this expected or not, but it is what I have experienced since day one.

mfleming · 03-04-2020, 02:24 AM

I always power off the 41CL THEN disconnect the serial cable usb from the pc THEN remove the serial jack from the 41CL. In that sequence I've never experienced an MMU reset (well, *almost* never). I believe there is a warning in Monte's build document about not removing the jack while the calculator is on because a momentary short is created when pulling the jack from the plug.

cdmackay · 03-04-2020, 02:32 AM

(03-04-2020 02:08 AM)Sylvain Cote Wrote: I do not know if this expected or not, but it is what I have experienced since day one.

thanks Sylvain!

cdmackay · 03-04-2020, 02:34 AM

(03-04-2020 02:24 AM)mfleming Wrote: I always power off the 41CL THEN disconnect the serial cable usb from the pc THEN remove the serial jack from the 41CL. In that sequence I've never experienced an MMU reset (well, *almost* never). I believe there is a warning in Monte's build document about not removing the jack while the calculator is on because a momentary short is created when pulling the jack from the plug.

thanks Mark.

Yes, that's exactly what I do, too; I should have noted in my first post that the 41CL is always OFF when inserting or removing the cable at either end.

It's odd that you don't see it, then. Perhaps small differences in spec over time, or just bad luck.

Not a big deal, as I said.

thanks both for the replies.

**rprosperi** · 03-04-2020, 03:18 AM

Unplug the serial cable from the PC before you unplug it from the 41CL. The tip is positive and when it is removed, if active due to being plugged-in, effectively shorts the bus (definitely not the correct terminology here) and disables the MMU. This is stated in the manual, but I too never found it and inquired here years ago when this was happening to me.

TL;DR - Unplug the serial cable from the PC first, and then you can unplug it from the CL without resetting the MMU. A common conclusion is it's easier to type XEQ "MMUEN" than trace the cord and unplug it from the PC... Smile

mfleming · (This post was last modified: 03-04-2020 06:21 AM by mfleming.)

(03-04-2020 12:47 AM)cdmackay Wrote: If it makes a difference, I use a Prolific USB-serial cable at the PC end (actually a Mac laptop).

To add a little detail, I use a Sabrent USB to serial cable with a genuine FTDI chip, which might make a difference over the Prolific chip. I also give the 41 a moments' pause (learned from similar past experience?) after turning it off, because the Maxim chip used for the RS232 interface in the 41CL doesn't seem to go dead immediately after power is removed. Charge retained in the P/S bypass cap? Who knows...

Edit: I'll have to check the datasheet, but I'm pretty sure the Maxim chip doesn't immediately disable the rs232 lines when a connected device is removed. Count to five before disassembly Smile

Ángel Martin · (This post was last modified: 03-04-2020 09:18 AM by Ángel Martin.)

I too suffer from the same (small) issue in two of my three CL machines - but the third one seems to be more rugged. Sometimes I first touch the base ring of the connector on the CL port with the tip of the jack before plugging it in, and then the MMU is not disabled. Note however that this is probably a bad practice electrically speaking, so I wouldn't suggest you do it!

My setup is a direct RS-232 port (yes, still a desktop PC with Windows-7)

cdmackay · 03-05-2020, 12:28 AM

(03-04-2020 03:18 AM)rprosperi Wrote: Unplug the serial cable from the PC before you unplug it from the 41CL. The tip is positive and when it is removed, if active due to being plugged-in, effectively shorts the bus (definitely not the correct terminology here) and disables the MMU. This is stated in the manual, but I too never found it and inquired here years ago when this was happening to me.

TL;DR - Unplug the serial cable from the PC first, and then you can unplug it from the CL without resetting the MMU. A common conclusion is it's easier to type XEQ "MMUEN" than trace the cord and unplug it from the PC...

thanks Bob; I tried to say that this is what I always do, but clearly I did a bad job of explaining, sorry.

anyway yes, I was aware of that, and always do that, but still get the MMU disabled.

cdmackay · 03-05-2020, 12:30 AM

(03-04-2020 06:04 AM)mfleming Wrote:
(03-04-2020 12:47 AM)cdmackay Wrote: If it makes a difference, I use a Prolific USB-serial cable at the PC end (actually a Mac laptop).

To add a little detail, I use a Sabrent USB to serial cable with a genuine FTDI chip, which might make a difference over the Prolific chip. I also give the 41 a moments' pause (learned from similar past experience?) after turning it off, because the Maxim chip used for the RS232 interface in the 41CL doesn't seem to go dead immediately after power is removed. Charge retained in the P/S bypass cap? Who knows...

Edit: I'll have to check the datasheet, but I'm pretty sure the Maxim chip doesn't immediately disable the rs232 lines when a connected device is removed. Count to five before disassembly

I'll try a long pause next time, thanks Mark Smile

I'll also try a different cable; I think I have an FTDI-based one somewhere.

cdmackay · 03-05-2020, 12:32 AM

(03-04-2020 09:15 AM)Ángel Martin Wrote: I too suffer from the same (small) issue in two of my three CL machines - but the third one seems to be more rugged. Sometimes I first touch the base ring of the connector on the CL port with the tip of the jack before plugging it in, and then the MMU is not disabled. Note however that this is probably a bad practice electrically speaking, so I wouldn't suggest you do it!

My setup is a direct RS-232 port (yes, still a desktop PC with Windows-7)

nice!

thanks Ángel; interestingly, it only happens for me when disconnecting. Connecting the cable never disables the MMU for me.

Agreed, it's a tiny issue, just wondered if I was doing something wrong. Doesn't sound like it.

thanks again, all!