Re: Apple brand II GS Ram card-- 1MB

[Rubywand <rubywand@swbell.net>]

Dennis Fenton writes ...
> 
> There are two jumpers on the Apple II GS memory card. If the card is fully
> populated should both jumper blocks be present or absent? Or, should one
> be on and one off? If so, which?
>

     Both jumpers should be present. The standard Apple IIgs 1MB Memory
Expansion card can be usefully configured for 256kB, 512kB, and 1MB.


     For 256kB, the top left 8 sockets (i.e. the left half of the top
row) should be filled. No jumpers should be placed on the pins near the
lower right end of the board.


XXXXXXXX--------
----------------
                         O O (no Jumpers)
                         0 0


     For 512kB, the entire top row of sockets should be filled. The
bottom 
pair of pins should be jumpered.

XXXXXXXXXXXXXXXX
----------------
                         O O
                         0-0 Jumper bottom pair


     For 1MB, all sockets should be filled. The top and bottom pairs of 
pins should be jumpered.

XXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXX
                        O-O Jumper top and bottom pairs
                        O-O 

 
> Also, do all the chips have to be identical in speed as well as size?
> 

     Mixing speeds and types is fairly common. (Usually, users try to
have the chips in each 8-chip set as similar as possible in terms of
speed.)  The standard speed for the RAM used seems to be 120ns - 150ns.
If you mixed in a somewhat faster chip, say, 70ns, there should be no
problem.

     Size needs to be 256k x 1 and the type should be compatible with
the NEC D41256C DRAM-- like a Hitachi HM50256. (For some weird reason,
the 41256 number is also used by some makers for 32k x 8 SRAM chips; so,
you can not just order any "41256" RAM chip.)

     Alltech (760-724-2404) may still be selling a "1MB Expansion Kit"
of 24 256k x 1 DRAM chips for $24.00.    



Rubywand