Re: Apple II plus memory map needed + other help :)

[mjmahon@aol.com (Michael J. Mahon)]

andy welburn asked:

>Hi all..
>
>first post here.. so don't flame me, i have lookedm but i can't understand
>the memory maps and other information that i am finding..
>
>I have an apple 2 plus sitting here that i am trying to bring back to life,
>the power supply is good, that i do know, the cpu is running ok (no resets)
>but no video output..
>
>I fix video arcade pcb's all the time, and have a Fluke 9100 digital test
>system, and a 6502 pod.. i could do preliminary tests to work out whats
>wrong, if only i had a reliable memory map..
>
>for example, Missile Command (6502 based) is like this:
>
>0000-3FFF = ram
>5000-7FFF = Program ROM
>
>i'm only really interested in ram/rom locations as i can run tests on those,
>i don't need to know input ports or other stuff..
>
>The only other thing i need to know is if there's any banked memory or rom
>or something, need to know if and where the switches are..

First remove any plug-in cards from the eight "slots" at the rear of
the motherboard.  That simplifies the system to motherboard ROM
and RAM, which is:

   0000-BFFF = motherboard DRAM
   C000-CFFF = I/O (C000-C0FF) and I/O expansion ROM (in slots)
   D000-FFFF = motherboard ROM (standard RESET entry)

If the video refresh is not happening, then the DRAM is not being
refreshed either.

Best bet is a schematic and thorough tracing of video generator
timing.

-michael

 Email:  mjmahon@aol.com
 Home page:  http://members.aol.com/MJMahon/