It's 600XL time!

[stephen_usher]

*crosses fingers* I hope it's available, or at least the Gerbers and BOM for one so that you can build your own.

[rubber_jonnie]

*crosses fingers* I hope it's available, or at least the Gerbers and BOM for one so that you can build your own.

I did look around for gerbers etc, but not found any, though I have been very busy at work. Two separate people suggested Jürgen so keeping my fingers crossed.

[rubber_jonnie]

Well, I have ordered the Syscheck 2.2 card from Jürgen, all in price of €70 inc postage. Will still see if I can find out what's wrong in the meantime as he has to build it for me first!

[rubber_jonnie]

Very quick test at lunchtime as time was limited (I may have also posted this previously, I've lost track having this horrible cold), but if I remove the BASIC ROM from the 800XL, it starts as expected and as follows:

1. A blue screen appears with a white cursor and the machine makes its usual 'farting' sound.
2. After a short period of time, the self test menu appears as though option was pressed.

However in the 600XL with no basic rom, whilst I'd expect the same, I get the following:

A black screen, and the ROM/RAM self test starts if you press option, though just that test alone and not the self test menu.

Since the OS known good and works on the 800XL, and we know the first 8KB RAM works (Possibly at least 16KB if the RAM check is to be believed), which should be more than enough to run the self test, I'm thinking that the OS ROM is not being properly addressed beyond a certain range, but Star Raiders works because it doesn't need the OS ROM to go that far before it takes over, so it never gets an address that isn't working.

Clearly some addressing does work, and data out, or there would be no RAM/ROM test, but that addressing is clearly off since it should got to the self test first. I'm thinking I may break out the LA over the weekend since my dead test tool won't be here for a while.

[stephen_usher]

Sounds like a plan. Do the higher address lines look good when sampled on the ROM itself when you try to boot?

[rubber_jonnie]

Sounds like a plan. Do the higher address lines look good when sampled on the ROM itself when you try to boot?

They look fine on the scope, and they do seem to buzz out ok, but I have only looked once booted, so I need to compare to the 800XL at the ROM during boot.

I found some damage when I replaced the single wipe sockets, so there maybe something else I've yet to find.

[rubber_jonnie]

Ok, so my Syscheck2 cart is on the way, but I found time to take an LA dump of the 600XL and 800XL at boot with just the OS installed, so no basic meaning it should drop to self test after a blue screen with a cursor appears during boot.

Traces taken at the OS ROM address lines.

This is the 600XL, which just gives a black screen:

Screenshot 2022-03-07 at 00.02.57.png

And in contrast this is the 800XL:

Screenshot 2022-03-07 at 00.03.19.png

Something very strange here, because the 600XL looks really very different. 800XL sets all address lines high at the OS on power up, 600XL, well I just don't know what's happening, but it's definitely not the same.

This is just the first 9 address lines of 14 (A0-A13).

[stephen_usher]

Given that it’s doing strange things on power up, how does the system reset to a known state before running the CPU? Just wondering about the reset circuit, if there is one.

Also, did you try looking at the LA results during multiple power-ups to see if it’s consistent?

[Tomswork]

That pattern of the 600 looks very repetitive across the address lines. The 6502 has a simple timer to reset maybe the cpu is sitting in a no op condition


Tom

[stephen_usher]

Oh, just another thought. Have you checked the address and data line pull-ups? Having the behaviour change if a cartridge is inserted might point to iffy voltage on the buses.