Re: Update on Apple II rev 0 replica kits

["Bryan Parkoff" <nospam@nospam.com>]

Mike,

> The 6502 Hardware manual states that if powered on without reset, "the 
> contents of the latches, registers, etc. is totally random after power is 
> applied".

    Yes, I am aware of this 6502 hardware manual, but it is not accurate. 
How did I know?  I wrote about 20-40 hex codes.  I stored them into EPROM 
chip. After RESET was powered-up, $FFFC-$FFFD started at $F800.  $F800 
executed 20-40 hex codes.  It copied all the internal registers into RAM 
before it reached JMP instruction.  It went endless loop using JMP 
instruction.  My observation showed that all registers were set to ZERO.
    I don't believe that all internal registers were set to ZERO during 
RESET sequence.

> There is a clear input on the 74LS259 that controls graphics modes. This 
> driven by the 74LS00 at location A2.  I suspect that the 74LS259 powers up 
> faster than the heavily loaded output of the 74ls00, so that the outputs 
> of the 74ls259 end up powering up in low state, resulting in text mode. 
> Note that later rev boards that have problems in the processor section, 
> also power up in text mode.  See my repair page for an example screenshot.

    Thanks for explaining.

Bryan Parkoff