7 replies to this topic

[Ralphy Rocket]

Hi,

I've been fooling around trying to get a 1 Meg SIMM into my 800. The atari seeing 48K like normal, so far. I ANDed the /SEL lines to get it in on one slot. I havent wired up the additional multiplexers for the other address lines yet (I'm confident 'bout that part) My problem right now is how to generate /CAS without using the 74ls158 (stock 16k board). How can I tune up the signal after that capacitor and coil (delay) to generate /CAS?????

Thanks in advance
Ralph

PS I'll post more details soon, I'm just so pressed for time...

[warerat]

The stock 16K board is just inverting /RAS to generate /CAS.

If you look at the output from the 'LS10, /RAS is the active-low output. Past the RL delay, the third mux in the second 'LS158 has bus A tied high, and bus B tied low. /RAS is tied to the data select, and as /RAS is active low (bus A), the output will be high (inverse). So they're just using one of the muxes as an inverter.

How will you be doing the bank select? The Axlon method?

Ralphy Rocket, on Thu Dec 22, 2005 5:29 AM, said:

Hi,

I've been fooling around trying to get a 1 Meg SIMM into my 800. The atari seeing 48K like normal, so far. I ANDed the /SEL lines to get it in on one slot. I havent wired up the additional multiplexers for the other address lines yet (I'm confident 'bout that part) My problem right now is how to generate /CAS without using the 74ls158 (stock 16k board). How can I tune up the signal after that capacitor and coil (delay) to generate /CAS?????

Thanks in advance
Ralph

PS I'll post more details soon, I'm just so pressed for time...

Edited by warerat, Mon Dec 26, 2005 3:26 AM.

[Ralphy Rocket]

If you look at the output from the 'LS10, /RAS is the active-low output. Past the RL delay, the third mux in the second 'LS158 has bus A tied high, and bus B tied low. /RAS is tied to the data select, and as /RAS is active low (bus A), the output will be high (inverse). So they're just using one of the muxes as an inverter.

How will you be doing the bank select? The Axlon method?

Hmmm??? I tried inverting it but It didnt work. I think because /Ras needs to be low when /cas goes low, so I think just inverting it wouldnt solve it. However, It turns out I have to use 2 more multiplexers chips anyway, and I only need 3 multiplexer out of one chip, that leaves me the one to generate /cas with. We'll get back to this problem if I decide to go to 4 MEGS!!!!!

Anyway....I don't know what the standard memory upgrades are in an 800, I'm just doing this project to exercise my brain. I used a 74ls138 decoder to break up the PIA address space into eight 32 byte segments, The first one is, of couse PIA, the second is for an 8 bit latch, Thats gonna be my bank select port. and I still have 5 more 32 byte segments to map other hardware. I'll stick an IDE drive in there somewhere. Maybe a small LCD screen and now I have 2 slots open, there the memory used to go.....any ideas what to stick in there????


Ralph

[Ralphy Rocket]

ALL RIGHT!!!!

I have the 1 Meg simm up and running!!! PB4 enables bank switching. An 74ls373 mapped to address 54048 selects the banks using bits 2-7. I used bits 0 and 1 for 2 LEDs (just for kicks and testing since I don't have a scope)or I can use those 2 bits for 4MEGS, one day. So right now its giving me 63 16K banks. I think the 64th(or first) bank should be the same as the main, but I think im getting something else there thats not right...I'm not gonna try to correct it. its already too much chips on the board. 63 16k banks is enough

I was wrong about not needing to figure out /CAS. I had to use a 5th multiplexer just to handle this issue. I guess it doesnt matter. I'm still gonna have to use ANOTHER chip anyway. I'll get some pics and schematics up soon

Ralph

[Almost Rice]

Ralphy Rocket, on Wed Dec 28, 2005 12:05 PM, said:

I'm still gonna have to use ANOTHER chip anyway. I'll get some pics and schematics up soon 

Ralph

Cool, is the upgrade compatible with an existing upgrade? I was looking into doing in to my 800xl. I just never got around to it.

Keep us updated.

[kevin242]

Would it be possible to get this working on a 400?

[doctorclu]

Ralphy Rocket, on Wed Dec 28, 2005 12:05 PM, said:

ALL RIGHT!!!!

I have the 1 Meg simm up and running!!! PB4 enables bank switching. An 74ls373 mapped to address 54048 selects the banks using bits 2-7. I used bits 0 and 1 for 2 LEDs (just for kicks and testing since I don't have a scope)or I can use those 2 bits for 4MEGS, one day. So right now its giving me 63 16K banks. I think the 64th(or first) bank should be the same as the main, but I think im getting something else there thats not right...I'm not gonna try to correct it. its already too much chips on the board. 63 16k banks is enough

I was wrong about not needing to figure out /CAS. I had to use a 5th multiplexer just to handle this issue. I guess it doesnt matter. I'm still gonna have to use ANOTHER chip anyway. I'll get some pics and schematics up soon 

Ralph

Congrats on getting that working. The Atari 800 is one of my favorite Atari anything. Let me know if you are up for doing more upgrades, I have been looking to upgrade my own Atari 800 one of these days.
Technically the Atari 800 is not capible of using anything above 48K for a glorified ram disk (like MyDos can do) but hey, would still be nice to say "I have one meg in my Atari 800."

[Ralphy Rocket]

Hey fellas,

Sorry, its not compatible with any thing. I suposed programs could be patched.....PB4=0 to eneables banking (like on the XL) address $D320 to bank select. Which apears as a 16k bank at address $4000 (like the XL)

It will work on a 400, cause its the same thing

It did get a little messy, not all the signals are in the memory slot. So I used the unused pins and pins I didn't need anymore to get those signals into the 1 meg card, plus I had to hack the motherboard a bit. Its a FRANKENSTEIN!

Now a bit of bad news (if you can call it that) when I select bank 0 I get $0-$3FFF at the bank space, and when I select Bank 16 I get $4000-7FFF (like if I wasn't banking) SO WHAT!!!!! I still have 62 16K banks. I just have to remember 2 are invalid. I'm not EVEN gonna try to correct it...62 16K banks!!! thats 20 1/2 800's worth of memory. (Remember I'm 3 wires away from 4 Megs..I just cant find a simm!)

ANYWAYS! Enough RAMbling (ha ha) Tonight I'll start on the harddrive interface (I already have Sijmen's MyIDE in my XL..IT ROCKS!!!) but on the 800 I'm gonna map it somewhere else in memory and use all 16 bits. Once I stick in all the goodies I want in there, and organize, clean up, and get a procedure going, then I'll do another one definately! (Doctorclu)

Ralph