Path: utzoo!utgpu!water!watmath!clyde!burl!codas!killer!elg From: elg@killer.UUCP (Eric Green) Newsgroups: comp.sys.cbm Subject: Re: Cartridge Port Message-ID: <3021@killer.UUCP> Date: 22 Jan 88 04:12:21 GMT References: Organization: Bayou Telecommunications Lines: 29 in article , tw0i+@andrew.cmu.edu (Todd Andrew Williamson) says: > Can anyone give me a comprehensive idea of what the game and exrom lines on > the cartridge port of the 64 do? I think I have a pretty good idea, but I'd > like to be sure. I heard a nasty rumor that if the game line is held low on > startup, the 64 goes into a "Max machine" mode, with like 4k of RAM or > something. I tried all of my usual sources, but I couldn't find any > information on the PLA chip. Any information would be appreciated, either a > post or EMAIL. Look on pages 263-267 of the Programmer's Reference Guide. Yes indeedy, if you pull down the *GAME line without pulling down the *EXROM line, it goes into "ULTIMAX video game memory map". Interesting thing about Ultimax mode... only 4K of RAM is accessible. Period. You can't read any other RAM, and, what's even more mystifying, you can't WRITE any other RAM. Boggles one's mind... "WHAT the HECK is THAT in there for?!". 'Nother interesting thing is the snafu of p266 (bottom), the 16K cartridge memory map, and page 265 (bottom), the 8K BASIC expander memory map. Look carefully at LORAM and HIRAM for both (those are two bits in location $01, see the memory map). They're identical! In actuality, one is supposed to be LORAM=1,HIRAM=0. Something else interesting is that my copy of Abacr*p's "The Anatomy of the Commodore 64" has those very same memory maps in it -- complete with that error! So much for proof-reading...... -- Eric Lee Green elg@usl.CSNET Asimov Cocktail,n., A verbal bomb {cbosgd,ihnp4}!killer!elg detonated by the mention of any Snail Mail P.O. Box 92191 subject, resulting in an explosion Lafayette, LA 70509 of at least 5,000 words.