Memtop issue with cartridge

[Marius]

Hi

 

I have a strange issue.

 

I have an original Assembler Editor cartridge. When I type "SIZE" at the prompt. Memtop is 9C1F. That's the right value.

 

This cartridge is build upon 2 4kROM chips.

 

Since I don't have that eproms, I put in another (but same) PCB one eprom (2764) with also the Assembler Editor rom. Everything works fine, except one thing.

 

I have less memory! Memtop is now 7C1F.

 

What is causing this? I don't want that ofcourse. Is there a fix?

 

Thanks

M.

[Rybags]

Are you using the board from a 16K cart?

 

Seems the cart is identifying itself as occupying the $8000-$9FFF area.

 

RD4 line controls that, so should be disconnected on your board.

 

http://www.atarimax.com/jindroush.atari.org/acarts.html

[Marius]

Are you using the board from a 16K cart?

 

Seems the cart is identifying itself as occupying the $8000-$9FFF area.

 

RD4 line controls that, so should be disconnected on your board.

 

http://www.atarimax.com/jindroush.atari.org/acarts.html

 

You are TOO good! That was it. I really thought I had same PCB's... but this line indeed was not on my orignal cart. Now it works.

 

THANKS Rybags. You get a +1 from my side!

 

Greetz

M.

[+Larry]

Wow -- I never realized that. I have made several "8K" eprom carts using the nice (U.S) Deico 8/16K eprom carts, but I never realized that my "8K" were effectively "16K".

 

I'm looking at one of those cart pcb's right now, and according to this diagram, I do find RD4

 

http://www.hardwarebook.info/Atari_8-bit_Cartridge

 

(same diagram as yours)

 

Any particular place to break the trace -- just someplace that is convenient and can be jumpered easily to restore if needed?

 

-Larry

 

 

 

Are you using the board from a 16K cart?

 

Seems the cart is identifying itself as occupying the $8000-$9FFF area.

 

RD4 line controls that, so should be disconnected on your board.

 

http://www.atarimax.com/jindroush.atari.org/acarts.html

[Rybags]

I'd say somewhere convenient and restorable.

 

You shouldn't need to ground that line either, since the default state of it is unconnected anyway.

 

Weird though that if someone made carts specifically for homebrew type applications that some sort of jumper system wasn't provided in the first place.

[BillC]

Wow -- I never realized that. I have made several "8K" eprom carts using the nice (U.S) Deico 8/16K eprom carts, but I never realized that my "8K" were effectively "16K".

 

I'm looking at one of those cart pcb's right now, and according to this diagram, I do find RD4

 

http://www.hardwarebook.info/Atari_8-bit_Cartridge

 

(same diagram as yours)

 

Any particular place to break the trace -- just someplace that is convenient and can be jumpered easily to restore if needed?

 

-Larry

 

 

 

Are you using the board from a 16K cart?

 

Seems the cart is identifying itself as occupying the $8000-$9FFF area.

 

RD4 line controls that, so should be disconnected on your board.

 

http://www.atarimax.com/jindroush.atari.org/acarts.html

I have some VLSI 16K boards, and also a couple Atari made ones as well, I got from B&C which have RD4 & RD5 ROM pins tied to +5V. The trace from the socket to the A edge connection runs up the right side of the back of the board. Cutting this trace allows a single 8K EPROM to be used in the right socket without using an extra 8K of RAM.

I have included a picture of the VLSI bare board showing which trace to cut.

.

[+Larry]

Thanks Rybags and BillC and Marius!

 

I scratched off a minute section of line "A" on the pcb and indeed it is now a true 8K cart, but very easy to reverse if needed. Interestingly, I had to scratch like heck to cut through the trace, even though the cut is only about .010" and the trace is even thinner.

 

I learn something new almost every day at this forum!

 

-Larry

 

I have some VLSI 16K boards, and also a couple Atari made ones as well, I got from B&C which have RD4 & RD5 ROM pins tied to +5V. The trace from the socket to the A edge connection runs up the right side of the back of the board. Cutting this trace allows a single 8K EPROM to be used in the right socket without using an extra 8K of RAM.

I have included a picture of the VLSI bare board showing which trace to cut.

.