Re: Old RAM cards protocol

[a3khan@sms.business.uwo.ca (Alimudin Khan)]

guertinp@saguenay.iro.umontreal.ca (Paul Guertin) writes:

> Hello,
>  
> I'm in the process of disassembling Locksmith 6.0's Fast Disk Backup and
> I need information about old "language-card-style" RAM cards for the
> Apple //.
>  
> Locksmith recognizes two kinds of RAM cards. One kind of card has two
> 16k banks, and the second bank is accessed by reading C08F twice. Does
> anyone regognize that card? Am I correct in thinking that C080--C083 and
> C089--C08B are the standard switches for the first 16k bank and that
> C084--C087 and C08C--C08F perform the same functions for the second 16k
> bank?

Hmm, just looked these up the other day.  First, these switches are for 
the language card, which is 16K.  The switches map the address space from 
$D000 to $FFFF to either ROM or the RAM on the language card; however, 
the space from $D000 to $FFFF is only 12K, so the other 4K is 
bank-switched in at $D000.  The switches are:

bank 1:
$C088 or $C08C     RAM, bank 1, write-protect RAM (in the language card)
$C08B or $C08F     RAM, bank 1, disable write-protect.  This switch
                   must be toggled twice to work.
$C08A or $C08E     ROM, enable write-protect on RAM
$C089 or $C08D     ROM, disable write-protect (must be toggled twice)

bank 2
$C080 or $C084     RAM, bank 2, enable write-protect
$C083 or $C087     RAM, bank 2, disable write-protect (toggle twice)
$C082 or $C086     ROM, enable write-protect
$C081 or $C085     ROM, disable write-protect (toggle twice)

Info from Gary Bond's 'Inside the Apple IIGS'.  The Apple IIGS Hardware 
Reference also details these switches.
>  
> The second kind of card can have up to 256k, in sixteen 16k banks. I
> think those are the old Saturn or Titan RAM cards. Unfortunately, I

[...]

> Finally, here's the code Locksmith uses when scanning slots to find
> RAM cards. I don't understand the part between 206E and 2083. What

[...]

Can't help you with these ones. Hopefully, someone with good knowledge of 
assembly language can.  Good luck!


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Alim Khan
a3khan@student.business.uwo.ca
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