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From: fred@cbmvax.UUCP (Fred Bowen)
Newsgroups: comp.sys.cbm
Subject: Re: trouble with 128 in 64 mode
Message-ID: <2443@cbmvax.UUCP>
Date: Thu, 1-Oct-87 14:46:14 EDT
Article-I.D.: cbmvax.2443
Posted: Thu Oct  1 14:46:14 1987
Date-Received: Mon, 5-Oct-87 08:31:58 EDT
References: <3495@rutgers.rutgers.edu> <1662@ulowell.cs.ulowell.edu>
Organization: Commodore Technology, West Chester, PA
Lines: 26

> All auto-start cartridges for the C64 contain 5 bytes of Auto-start code 
> starting at location $8004 (at least as I can remember). These 5 bytes are
> checked by the computer at power-on.  When you plug a C64 cartridge into
> a C128, the 128 recognizes these bytes as being the 64 startup.  The 128
> mode auto-start uses a slightly different sequence of characters to indicate
> that they are 128 mode cartridges.

Wrongo.  As I posted earlier, the C128 at powerup is running in Z80 mode.
The Z80 looks at the hardware lines to see if there is a cartridge there,
or to see if yer finger is holding down the C= key.  It does not address
the cartridge and look for 'CBM80' out there- that is done by the 6510
processor long after it's already in C64 mode.

The C128 cartridge has a different signature because it was more flexible-
the card tells the Kernel when to call it- before or after (or both)
initialization is complete, etc.  It is similar to the Plus/4 routine-
cartridges are 'logged in', allowing one card to see if another is there
via its ID.

--
-- 
Fred Bowen			uucp:	{ihnp4|rutgers|caip}!cbmvax!fred
				arpa:	beats me
				tele:	215 431-9100

Commodore Electronics, Ltd.,  1200 Wilson Drive,  West Chester,  PA,  19380