How did the Compyshop ram expansion differ from Rambo, etc.?

[+Larry]

Title says it all -- I've searched, but can't find any descriptions of how the Compyshop ram expansion for XE/XL was configured.

 

-Larry

[+CharlieChaplin]

Well,

 

There are several Compyshop XL/XE RAM enhancements, they made several types, one for each XL or XE type, e.g. one for 600XL, one for 800XL without Freddie, one for 800XL with Freddie, one for 65XE, one for 800XE, one for 130XE. Afaik, all of them use blocks 26AE, while Rambo and compatibles use blocks 8ACE; this Compyshop config. had the advantage that one could use sep. Antic access, but it was not built-in, the few Atarians that wanted it had to do it themselves...

 

Compyshop XL, Compyshop XE, Megaram 1, Megaram 2 and Megaram 3 (256k) use these banks:

23, 27, 2B, 2F, 63, 67, 6B, 6F, A3, A7, AB, AF, E3, E7, EB, EF (blocks 26AE)

 

Rambo, TOMS, Atari Magazin (AM), Peterson, Buchholz, Newell and others (256k)* use these banks:

83, 87, 8B, 8F, A3, A7, AB, AF, C3, C7, CB, CF, E3, E7, EB, EF (blocks 8ACE)

* when adding +256k RAM to the existing 64k base RAM... (it is a bit different, when 64k base RAM gets replaced with 256k RAM)

 

Thus Compyshop and Rambo have 50% the same banks (blocks A and E) and 50% different banks. The above counts for RAM enhancements that add +256k RAM to the existing 64k base RAM for a total of 320k memory. There are also RAM enhancements that replace 64k RAM with 256k RAM for a total of 256k RAM (64k base RAM and 192k XRAM then) - afaik, some (all?) of the Rambo, Newell and Buchholz types are among them. The emulators (Atari 800 and others) seem to support only the RAM enhancements that add +256k RAM (320k RAM total). So, if you choose Rambo in the emulator, then you have 320k memory and blocks 8ACE, whereas with a real Atari and Rambo enhancement you sometimes just have 256k RAM and blocks ACE or 8AE (depending on the age and the design of your enhancement)...

 

-Andreas Koch.

[+Larry]

Thanks, Andreas! Exactly what I was looking for, and really good info.

 

A couple of other related questions -- 1) Used PORTB for banking control? 2) Any reason to believe that ram-under-rom used in some programs would not work? e.g. Turbo Basic XL.

 

-Larry

[+CharlieChaplin]

Well,

 

1) both Rambo and Compyshop RAM enhancements did use port B for banking control afaik. The banking bits ($D301) for Compyshop are: 2, 3, 6, 7 and the banking bits for Rambo are: 2, 3, 5, 6. And regarding question 2) I do not know for sure... at the moment I use a 512k RAM enhancement in my 800XL (blocks 02468ACE with 4 banks each) which therefore has both Compyshop and Rambo banks available and TB XL still works ok, so there should not be a problem.

 

[speculation on] But maybe RAM under OS ROM is a problem for those RAM enhancements that replace 64k RAM with 256k RAM (then 64k base RAM, 192k XRAM), I do not know, since I never had such a RAM enhancement... [speculation off]

 

Anyways, an awful long list of A8 RAM enhancements, software that supports XRAM and software that requires XRAM can be found in the A8FAQ. But since no-one reads this FAQ, I did not update these lists for quite a long time... -Andreas Koch.

 

-Andreas Koch.

[Rybags]

PortB control should be the case for all legacy XL expansion systems that put the extra Ram @ $4000-$7FFF

 

Ram under Rom - a potential hazard with some expansions is they could remap the Ram that normally appears elsewhere into the $4000 window - e.g. $C000 Ram appears at both places. If a program that uses extra Ram doesn't test for this condition then it could be cause for problems.