Atari 800XL starts with selftest

[Marius]

Hi

 

One of my 800XL's is having strange issues. I was using it with a custom rom, that had not the "checksum" routines, so the Atari worked great... untill I tried to enable basic, which resulted in a crash.

 

Now I installed the default OS and the Atari selftest starts, and I have one bar RED.

 

I'm pretty sure that:

 

The BASIC ROM = OK

 

The OS ROM = OK

 

Since I had problems with going to basic with the Custom OS Rom, I was wondering:

 

Which parts are involved with the Basic Rom?

 

I had a blown LS08 in this computer (static electricity?) so I replaced it, and the computer started again. But it was not enough fix...

 

Anyone has an Idea

 

RAM = OK

 

Where to start?

Greetz

M.

[Marius]

Hmmm I replaced the 20 pins PAL C061618 ... is this the MMU?

 

That was the trick.

 

I was wondering: is this part replacable by a GAL? Has someone JEDEC file for that?

 

And which GAL to use?

 

Thanks

M.

[+Guitarman]

From another source.

 

The Atari MMU is a custom MMU chip for the Atari 8-bit computers. It enables access to the hardware registers on ANTIC, GTIA, POKEY and 6520 PIA. The later XL/XE MMU (C061618) also selects OS ROM, Atari BASIC ROM, self-test ROM and LEDs in the 1200XL. The user cannot directly manipulate the Atari MMU, but selects the various ROMS and memory via the memory-mapped hardware register known as PORTB (5401710 or D30116). Atari changed PORTB from an input port on the 400/800 machines to an output port on the XL/XE machines, leaving two joystick ports instead of four on the XL/XE machines. By setting and clearing specific bits in PORTB, the user can access either the ROMs or memory location.

[flashjazzcat]

Hmmm I replaced the 20 pins PAL C061618 ... is this the MMU?

 

That was the trick.

 

I was wondering: is this part replacable by a GAL? Has someone JEDEC file for that?

 

And which GAL to use?

Here you go:

 

mmupal.zip

 

You need a 16v8. Useless to me, since although I have GALs, the crappy eBay programmer won't write them.

[Marius]

I ihave the g540 I guess that one does the trick...

[santosp]

After one year from original post, the same issues here on my 800XL. What a pity not to see this thread earlier. One day with much effort measurements etc. I believe cause it should be done a "tech attachment".

A big thanks to flashjazzcat for the file.

Edited July 27, 2012 by santosp

[+tf_hh]

Hi,

 

Marius, do you still need a replacement? I can you send one or two, I have enough 16V8 and to the netherlands it´s cheap shipping.

 

Jürgen

[+bob1200xl]

You can program a PAL from the file, can't you? Usually, the programmer sets up the device as a 16V8 in 16L8 mode. The file is actually a 16L8 file and should work fine on a 16L8. (use a quarter-power 16L8)

 

Bob

[Roydea6]

I also have an 800xl that is going to selftest. And I was wondering if the MMU I took out of the 130XE to install a Ultimate1 would work in the 800xl.

[atari8warez]

I also have an 800xl that is going to selftest. And I was wondering if the MMU I took out of the 130XE to install a Ultimate1 would work in the 800xl.

 

Yup, it would.