Atari 800xl Missing Last 8 Bytes of RAM?

[+xucaen]

I just replaced these 4 chips:

U2 IC Decoder C061428

U3 IC Mem Mngt Unit (MMul B) C061618

U4 IC (8kx8) Basic ROM RevB C060302

U5 IC (16kx8) OS ROM C061598

I had been getting red ROM bars in the memory test. Now ROM is green, RAM is green - everything looks good except the last 8 bytes of RAM are missing. Is this normal? I thought the 800xl had 48 bytes of RAM.

If you are interested in the back story, see this thread: http://atariage.com/forums/topic/280756-super-stand-alone-system-test-shows-errors/

[flashjazzcat]

The BASIC ROM accounts for 8KB (kilobytes, not bytes) and the operating system is 16KB long, which added together make 24KB. 64 - 24 = 40, which is the number of RAM blocks you're seeing there.

 

Everything looks good.

[SoundGammon]

Turn off the power, hold down Option button, power on.

 

The screen for testing should come up, not basic.

 

Start memory test and the last 8 blocks should show up!

[+xucaen]

Turn off the power, hold down Option button, power on.

 

The screen for testing should come up, not basic.

 

Start memory test and the last 8 blocks should show up!

 

Indeed, you are correct. I was able to see those last 8 bytes. Thanks!

Everyday I learn something new about my 800xl.

[+Nezgar]

1 block = 1 Kilobyte (1024 bytes)

[+xucaen]

1 block = 1 Kilobyte (1024 bytes)

 

Yup, I got confused.