400 Memory upgrades

[ClausB]

The XL OS uses PORTB to switch RAM, so you would give up two of the 400's joystick ports, and you would have to add even more circuitry to switch between RAM and ROM.

 

 

Can't you also upgrade the OS so you don't have to split up the RAM upgrade? Or is due to a preference to keep the OS ROM stock?

 

[Jeffrey Worley]

On 5/6/2016 at 9:08 PM, KLund1 said:

This looks just as complicated. I'll have to read them both more carefully with a 400 open so I can follow along on the hardware as I read the directions.

I work a frys,and get the parts for near free, IF we carry them. Big IF.

I know we do not have the 74LS158, or the drams ic's. Mouser, Digi-Key, and Jameco for those.

But we should have the cap, and resistors, but I do not know enough about there descriptions to find the right ones. If you have a couple extra minutes, could you take a quick look, and send a link if you find the right ones?

Thanks for all your help!

A note on the Crowell/Davies 48k Atari 400 mod.  I learned this weekend the hard way, that this mod REQUIRES 74LS parts.  You cannot substitute S or F parts for LS.  The designers exploit the slow gate delay of this line of chips to make the mod work.  It is not good practice to do so, but that's how it works, so use LS parts.  If you have changed any parts on your ram boards prior to doing the upgrade, say, replacing a 74ls244 with a perfectly good 74F244 or the LS158's with another line of chip, you will have to re-substitute for the LS version or it just won't work.  Probably it will give you a black or a red screen on power-up, but I made versions this weekend that worked for 32k and then when the last bank was accessed it would crash in spectacular ways.  When testing make sure to use something really memory intensive.  The best for me were Spartados X, of course, Gauntletak, and Koronis Rift.  If it will run these well then you are in clover.

 

Claus Buckholz also did a 48k mod that can itself be modded to 64k.   The document usually includes both the mod and the mod-on-mod information.  I've not done that one yet, but I have a 400 that does not like the Crowell/Davies, which I hope will like Claus'.

 

best,

 

Jeff