Casio CZ/ VZ/ FZ - Pro Series

Hi Scott,

Thanks for the sacrificial ROM scan!

Regarding card detection, all that the VZ does to detect a card, 
whether a ROM or RAM, is check to see if pin 44 is low (grounded). If 
so, then the software allows the the data lines to be read, again, 
either RAM or ROM. 

To activate the RAM, pin 32 connects a high signal from the VZ port 
to the CE (Chip Enable) pin on the RAM chip, via a NOR gate chip, 
which pin 35 (high) also operates.  The ROM chip is disconnected from 
both these pins, as it is always enabled.

So the only difference between the 2 cards seems to be the extra 
address line RA15, which is connected to the highest address line A15 
on the ROM chip, but not connected to anything on the RAM chip. I 
don't know what means the VZ has to display "no bank", as you say, it 
would be interesting if someone could put in their RAM card and 
switch through the banks and see what it displays. 

In any case, I don't think the VZ sees any difference between a ROM 
and a RAM, except that it will fail to write to a ROM because the 
ROM's write line is not connected (and wouldn't work if it was, 
anyway.). This being the case, using a larger RAM  chip will give you 
an extra bank WITHOUT DIP switch selectors for extra address lines, 
because you can use RA15, which is disconnected on the RAM card, but 
is utilised on the ROM, being 2x larger than the RAM. For even more 
banks, you will need DIP switch selectors though.

Cheers, Graham




--- In CZsynth@yahoogroups.com, "Scott Nordlund" <gsn10@...> wrote:
>
> >I just got sent a photo of a ROM card opened up. There is not much
> >difference with the RAM and ROM PCB, the RAM has more etchings and
> >tracks in it for an extra chip that does switching of the CE (Chip
> >Enable) pin, and also the WE (Write Enable) pin, both of which the
> >ROM doesn't need. And a few other differences in the pin track
> >layouts to the RAM chip, but that's it. I've uploaded a schematic 
for
> >the RAM card in the FILES section on this site.
> 
> I think that was probably my ROM card, actually.
> 
> >Regarding having a larger chip, the schematics show already that it
> >was made to accommodate a chip 2x as large as the one used, there 
is
> >a spare address line not used on the connector. This is for the ROM
> >chip, which is 2x larger than the RAM chip (which is why it has an
> >extra bank of sounds) - The ROM is 512k and the RAM is 256k. It 
would
> >require no more effort than dropping in a 512k RAM chip and hooking
> >up the extra address line. As you say, an even larger chip can be
> >installed and the highest address lines switched with a DIP switch 
to
> >get extra banks.
> 
> Referring to the service manual... apparently a 2-bank RAM card was 
never 
> released.  When the VZ detects a RAM card, the highest address bit 
is 
> disabled (unless someone wants to modify the OS).  To access both 
banks (as 
> it would be useful to have 192 online patches), the VZ needs to 
detect a ROM 
> card.  In this mode, it would be impossible to write patches, and 
likely it 
> would have to be switched off when changing this to avoid crashing 
things.  
> But, if it can be determined how the VZ detects the card type, it 
could make 
> things a little more interesting.  From the diagram, it seems like 
only the 
> CD (Card Detect?) pin could determine this... but my scan only 
shows the 
> component side of the board, and that pin connects to something on 
the other 
> side.  This pin is grounded for a RAM card, so inside the VZ it's 
probably 
> just pulling down a high value.  But if that's the case, I'm not 
sure what a 
> ROM card could do differently.... I can take my card apart again if 
> necessary (though it's sort of damaged enough already...)
> 
> Actually, maybe this should be verified.  If anyone has a RAM card, 
I would 
> appreciate it if this could be tested:  When a RAM card is inserted 
and the 
> CARD button is pressed multiple times, does it switch banks between 
CARD (1) 
> and CARD (2)?  If it does, that means it is actually using the 
highest 
> address bit, but since it's not connected, it's still just looking 
at the 
> same data.  Seems like it would be bad design to do it this way, 
but it's 
> possible.  I suspect a RAM card just shows up as CARD, with no 
indication of 
> bank.
> 
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