Atari 800 Ram Question

[Scooter83]

I got an atari 800 in the mail and I came across in the system a RAMCRAM 32K chip in it. The setup in the ports are :

 

< 10K ROM CHIP>

< 16K RAM CHIP>

< RAMCRAM 32K>

< OPEN SLOT >

 

The RamCram says that it goes behind the 16K and totals 48K. Is there anyway to toss another 16K ram and max it out at 64K? I would think if the RAMCRAM is correct the system would ignore the last 16K of Ram. Just wondering if you could add more and get away with it.

[mimo]

Nope 48k Max without surgery.

Get an incognito board for a full fat Meg of ram

[Scooter83]

Thought so figured I'd ask anyway

[+Faicuai]

Absolutely.

 

By all means, don't wait any longer and get your Incognito copy, and realize the unique and full potential your 800 has to offer.

 

Here are some specific comments, and how cleaned-up your expansion bay will look, after performing this (simple) upgrade:

 

http://atariage.com/forums/topic/212773-incognito-install-a-collectors-perspective/

 

Enjoy!

[ClausB]

I designed a one-chip circuit that can map a 16K RAM in slot 3 to the top of memory, under the OS ROM, like an XL. If anyone is interested I could post it.

[pedalpowered]

I designed a one-chip circuit that can map a 16K RAM in slot 3 to the top of memory, under the OS ROM, like an XL. If anyone is interested I could post it.

 

Could this perhaps be incorporated into a new version of the Incognito? I'm assuming that somehow this works with OS B.

Edited June 30, 2013 by pedalpowered

[ClausB]

No, Incognito has its own XL/XE compatible RAM. This is for those who would rather not open the 800's case. It is wired to the RAM board and OS board and the third joystick port. The OS ROM is not changed but you could load the XL OS into the top RAM.

[AtariGeezer]

I designed a one-chip circuit that can map a 16K RAM in slot 3 to the top of memory, under the OS ROM, like an XL. If anyone is interested I could post it.

 

I would be interested to see this mod

[ClausB]

The circuit assumes 16K in slot 1, 32K in slot 2, and 16K in slot 3. The chip should go on the slot 3 board, with 2 wires to the OS board and 1 wire to PORTB. It's a 74LS253 dual 4-1 tri-state multiplexer. (Multiplexers are great because they can implement multi-variable logic functions, a sort of poor-man's PAL. I've used some in my old RAM upgrades. Woz used a bunch in the Apple II.) The circuit also has two 4.7 kOhm resistors and a Schottky diode.

 

No time to draw it, so here's a connection list:

IC1: 74LS253
R1, R2: 4.7 kOhm
D1: Schottky diode

Vcc: IC1-16; IC1-12; Z501-14; R1; R2
Gnd: IC1-8; Z501-7
PB0: IC1-1; IC1-15; A102-10 or J112-1
A11: IC1-14; Z503-11
A12: IC1-2; Z503-5
-S6: IC1-13; IC1-11; IC1-10; A402-20
-S7: IC1-3; IC1-4; IC1-5; IC1-6; A401-20
-SA: IC1-7; Z501-1; R1
-SB: IC1-9; Z501-13; R2
-SL: Z501-6; D1 bar end
-XL: D1 other end; Edge connector M

 

This is untested but if you build it I'll help you get it running.

 

Since the 800 OS sets PORTB to inputs, you have to run a small program to set PB0 to an output in order to enable RAM/ROM switching:

LDA #$38
LDX #1
LDY #$3C
STA $D303
STX $D301
STY $D303

 

Thereafter, writing $FE to $D301 enables RAM and $FF enables ROM, just like an XL.

[AtariGeezer]

Okay, cool, thanks :thumbsup:

 

I'll have to pull out my original 800 since it's the only one with a 32k card...

[a8isa1]

I designed a one-chip circuit that can map a 16K RAM in slot 3 to the top of memory, under the OS ROM, like an XL. If anyone is interested I could post it.

Claus, I have a bone stock 48K 800 (except one of the 16K boards is a modified 8K board, ala an article in Analog Computing).

 

Is there a way to adapt your circuit to use the right-hand cartridge slot for that additional 16K, preferably using static RAM? I don't mind a few wires if I don't have to permanently modify the 800

 

I don't own any cartridges that use the right-hand slot.

[ClausB]

Yes. You could use the same circuit as above to map the top 16K (under the OS ROM) to the slot 3 board and map the next 16K (the cart ROM space) to an SRAM in the right cart. I can post a connections list if you want to build it.

[ClausB]

For the SRAM cart you could use something like this:

http://raster.infos....art/ramcart.htm

[ClausB]

The Schottky diode above must have a forward voltage drop < 0.4 V and a peak reverse voltage > 5 V. If that is too hard to find then add a 74LS09 chip instead and wire just one gate.

[a8isa1]

For the SRAM cart you could use something like this:

http://raster.infos....art/ramcart.htm

Santosp was selling a revised version of C.P.U.'s RAMCART. I don't know if he has any left.

 

I've had a homebrewed SRAM cart for years. It's just a multi-cart, hardwired at 16K. Can't remember if I connected cart pin A or S for phi2. (I must have it right though because pin S is RAS on 800).

 

It's an ugly thing. just a free floating circuit jammed into a shell

 

For this application I'd have to leave off RD4, RD5, /S4 and /S5. Pull A13 from somewhere. Add your circuit.

 

Are there any caveats? (I like to tinker but I don't know hardware).

 

Thanks, Claus

 

-Steve

[ClausB]

Leave your RAMcart as is, using /S4 and /S5 in the left slot. Modify your 16K RAM in slot 3 to use /S6 and /S7 with the circuit above, slightly modified. Lift Z501 pins 1 and 13 from their socket before connecting to them. You can avoid the diode by connecting Z501-6 to Z403-5, lifted from its socket, on the OS board.