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Re: Apple II ROM

Patricia Shanahan wrote:

Michael J. Mahon wrote:


Patricia Shanahan wrote:


Inspired by a History of Computing course I'm auditing, I dug my Apple
II out and powered it up.

It displays a screen with "Apple ][" at the top, otherwise blank. Reset
puts it in the monitor, which works correctly. It fails to enter Basic
or the mini-assembler.



So typing "Ctrl-B, Return" at the monitor prompt does not get you
to the BASIC prompt?



Correct. Also, "F666G" followed by a return does NOT take me to the
mini-assembler.


What, exactly, *does* it do when you enter these commands?


I am following the directions from the Reference Manual that came with
it, and as far as I remember everything worked the way it said in 1979.



The original (non-Applesoft) Apple ][ did not initialize BASIC
automatically.  It had to be cold started from the keyboard.


I've used the monitor to display ROM contents. The Monitor ROM, F800 and
up, matches pieces of code in the Reference Manual. The remaining ROMs
contain what looks like junk, and do not match Reference Manual listings. 

 From the functioning monitor, and good readouts from monitor ROM, I
conclude that the ROM address and data paths work. That makes me think
that the junk data from the other ROMs is due to failure of the ROM
chips themselves.



Although this is possible, it is not a likely failure.



Can you suggest alternative explanation for the symptoms, or tests I
should do to confirm or reject the ROM hypothesis?


You might try listing parts of it using the monitor.

For example, if you list $F666, does it look like the mini-assembler?

Since the monitor is in the same type and vintage ROM, it should
be expected to be in the same general shape as the rest of the
ROMs--which is why I suggested the improbability of their failure.


One of my friends, an electronics technician, suggested that some types
of ROM in use in the time period did tend to lose their data with time,
and it is a 27 year old computer. I don't know if that applies to the
ROM used in the Apple II.


I certainly doesn't seem to be a common problem.

It is possible to adapt 2716-type ROMs to the Apple ][, and that
would offer a possible means of replacement, as well as a definitive
proof that the ROMs were faulty.

You could also try installing the ROMs in another ][ or ][+ to see
if that moves the problem...

-michael

NadaNet networking for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

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