I pulled out my 800XL to try and get it running so my wife could play a few cart games today. First thing I did was open up the case to make sure it didn't need a cleaning and that none of the socketed chips had loosed since I had put it away in storage.
Well, my BASIC socket is empty, and the OS Socket has a custom chip in it. I pulled apart the keyboard, cleaned the contacts on the ribbon, booted it up and ran some tests.
Since I didn't have a BASIC ROM I plugged in one of the two BASIC carts I have.
Here's what I got after doing a couple peeks:
Both BASIC Carts come up as Rev A, which is good enough considering I haven't gotten my 1050 setup again yet, so that's no biggie.
I googled around and found that the two other peek addresses would identify the OS rom for me, since I couldn't be sure it hadn't been replaced. Not sure how to test how to get the size of the thing to see if it's been appended to or anything.
From what I can tell, a response of 2 from 65527 means it's the 800XL ROM, and 255 from 65528 means I have to use the alternative tape loading procedure if I decide to use cassettes.
Is that all correct? Is there anything else I can do with an accessory-less computer to check any other possibilities of the ROM?