Re: Clock Card?

[mjmahon@aol.com (Michael J. Mahon)]

Bill Garber wrote:

>I tried ProDOS users.disk and it claims there is no
>time or date. I tried reading the eprom, however I am not sure
>if I should read C400 or CC00. They don't display the same
>info. It is a 2764 which is I believe 8k so I'm not sure how that
>would read since $100 is all that will fit in the slot memory.
>How do I find out where the firmware is loading into RAM?
>You would think just about any clock software would find it.
>ThunderClock software searches the slots, finds none. NSC
>looks for it and finds none of course since it isn't looking in a
>slot at all. ProDOS seems to find nothing. I don't know what to
>try next.

This clock card (the battery is a dead giveaway) was probably
produced before the Thunderclock and ProDOS.  (Checking
chip date codes and/or card copyright date might verify this.)

It has an unusual amount of firmware for a clock card.

Odds are, none of the firmware is loaded into RAM, but
the ROM is bank-switched into the $C800 space, probably
by using some of the extra port bits on the 6821.

In its "default" state, there is almost certainly slot ROM
code in the $Csxx space, and a perusal of this code would
reveal how the 6821 is manipulated.  It probably also uses
$C800.CFFx space, with the 2KB chunk of ROM mapped
in depending on the 6821 port settings.

Try disassembling the $Csxx space and see where it
leads you.

(BTW, the 5832 requires at least 2.2 volts to keep time, so
there should be two cells on the card...)

-michael

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