Hi Dave
A common failure item in these old machines is the RAM.
Any failure of the RAM makes things like subroutines fail
quickly.
Dwight
>From: "Dave Dunfield" <dave04a_at_dunfield.com>
>
>>> Deos ftp://ftp.funet.fi/ still exist? That used to be a good place for
>>> Commodore schematics and technical info,
>>
>>Yup, FUNET's still alive. <ftp://ftp.funet.fi:/pub/cbm> for the CBM stuff.
>>There's also a web-based version at <http://nic.funet.fi/pub/cbm/index.html>.
>
>Thanks guys - that helps a lot.
>
>+++
>
>Does anyone have "inside" information on exactly what the PET firmware does
when
>it starts up?
>
>I am still working on the same pair of SuperPET 9000's (one works, one does
not).
>Both machines have been stripped to just the base 6502 board.
>
>The "bad" machine plays it's tune and clears the screen - then appears to hang.
>(If you reset it with the monitor warmed up, you can see the screen fill with
>"garbage" and then clear - just like the working one).
>
>Code appears to be running:
>
> - If I remove the KERNAL rom, the startup beep does not occur, and the screen
> never initializes, so it looks like this ROM is executing.
>
> - After it appears to "hang", the code still seems to be running. Looking at
> the 74LS154 decoder which shows accesses within 4k boundaries, I see lots of
> accesses to 0xxx (probably page0 RAM), no accesses to intervening locations
> and lots of access to the ROM's, which follow a clearly identifiable
pattern.
> Removing any ROM prevents this from happening, with the machine just
"flailing"
> until it gets a HLT - so it looks like it may actually be running ROM code.
>
> - I can see accesses to the keyboard scanner.
>
>On the working machine, after accessing all ROM's as BASIC starts (and prints
it
>welcome message), it settles into a keyboard scan which appears to exist within
>the KERNAL and EDIT rom's - the BASIC ROM's are not accessed unless some
function
>is activated.
>
>The non-working machine appears to hang during the phase where it is accessing
all
>ROM's - it continues to do this indefinately.
>
>It looks like the system is hanging during the initialization of BASIC - it
never
>prints the welcome message (hangs with blank screen).
>
>So far I have been unable to determine what it is doing exactly - any info on
the
>startup sequence would be MOST appreciated!
>
>I have verified that the ROM's contain exactly the same code as the other
machine
>(I've seen several PET's fail with bad ROM's, however this does not appear to
be
>the case here).
>
>Regards,
>Dave
>--
>dave04a (at) Dave Dunfield
>dunfield (dot) Firmware development services & tools: www.dunfield.com
>com Vintage computing equipment collector.
> http://www.parse.com/~ddunfield/museum/index.html
>
>
>
Received on Tue Aug 10 2004 - 19:43:37 BST