Date   : Thu, 09 Nov 2006 15:10:16 -0000 (GMT)
From   : splodge@... (Richard Gellman)
Subject: Grrr.....annoying master cmos ram

> I've recently replaced the batteries on my master's CMOS ram but it still
> fails fairly regularly (quite often with "Bad Sum" messages on Break/CTRL
> Break and lots of *TIME oddities)

That's not necessarily a CMOS RAM thing. I've seen the "Bad Sum" error
come up after playing certain games that do oooo terrible things to
workspace areas of RAM.

Curiously, the Ahkter floppy disc user guide says of "Bad Sum":

"We have never seen the error occur, and don't believe it exists."

It is in fact a DFS error, but as the user guide implies, its never seen
in a genuine context.

As for the *TIME, I would concur with Ian's conclusion there. If the CMOS
chip acquires random data as a result of the batteries being replaced, it
will not necessary "correct" the clock back to sensible values. I've seen
a Master 128 display things like "Tue, $n Nov 1900 %0:4n:00" before now.

A quick statement of the form TIME$="<date>" should sort that.

> Does the actual CMOS ram often fail? If so is it easy to replace.  Would
> anyone have the correct chips to hand?

I've not known the CMOS chip to be unreliable. Usually problems occur due
to failing battery packs or a failure to CMOS reset.

As for replacing the chip, I'm afraid on this chip (Motorola/Hitachi
146818) is:

a) difficult to get hold of with visiting specialising sites (such as
those run by various members of this list) as this chip effectively *is*
the millenium bug* (its the chip that doesn't go past 1999, which was
installed into millions of PCs, Master 128s, and a number of other
systems) and thus is undesirable in the post-2000 era.

b) soldered directly onto the board, and thus very difficult to swap. Some
later (replacement only?) boards wered fitted with a chip socket for this,
but I've only ever seen one such board.

-- Richard

* Yes, I know there are other clock chips with the millenium bug, but this
one is particularly prominent as it was used in so many PC systems as well
as M128s.

>
> Cheers
>
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