Re: ROM 3 Questions

["Roger Johnstone" <rojaws@mac.com>]

In article <1evzxdp.nrjk3fwb8hxcN%dempson@actrix.gen.nz>, 
dempson@actrix.gen.nz (David Empson) wrote:

> The Visit Monitor and Memory Peeker CDAs are available on all ROM 1 and
> ROM 3 machines, but they aren't supposed to be visible until you go into
> the monitor and use the # command.

And of course you can also enable them using the SetStart control panel in
System 6.0.1, but they aren't available until after you boot the OS.


> There is a minor bug in the ROM 3 firmware which means that it doesn't
> initialize the memory location which determines whether or not these
> CDAs are enabled.  When you power on the computer, the vast majority of
> machines happen to start up with this location set to zero, so these
> CDAs do not appear until you use the # command.
>
> For a very small number of ROM 3 machines, this location happens to
> contain a different value when powered on (probably FF), so these CDAs
> appear at startup.
>
> This behaviour is an artifact of dynamic RAM - it tends to power up with
> a particular pattern of values, and this will be reasonably consistent
> for the same memory chip.
>
> I know that Mitchell Spector's ROM 3 has this particular behavioural
> glitch.  I only recall ever hearing about one other machine which does
> it.

Hmm, now that's something I had never heard of!

--
Roger Johnstone, Invercargill, New Zealand

Apple II - Future Cop:LAPD - Warcraft II
http://homepage.mac.com/rojaws
______________________________________________________________________

My software never has bugs. It just develops random features.