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From: John_A_Pham@cup.portal.com
Newsgroups: comp.sys.apple2
Subject: Re: 6502 Startup Process
Message-ID: <29596@cup.portal.com>
Date: 4 May 90 19:54:50 GMT
References: <139800008@uxa.cso.uiuc.edu>
Distribution: usa
Organization: The Portal System (TM)
Lines: 32

wogg0743@uxa.cso.uiuc.edu writes:

>You have to rig it so when the power comes on, the processor gets a
>RESET (you bring high the reset line, I think).  You could do this
>simply by providing yourself with a button that completes a circuit
>(thus giving you a reset button into the bargain, but also making this
>part of the manditory start-up process) or else rig a more complicated
>circuit to do this once ever time the power comes on (like Apple uses)
 
Not quite, reset on the 6502 and 658xx require that reset must be held low
for at least two clock cycles after Vdd reaches operating voltage from
a power down.  Also, you don't need to use a fancy 555 for generating 
a reset upon power up,  try a resistor, cap and a diode (a switch for those
hardware/software problems)
.
     +5v----------+--+             
                  \  | 
                  /  - 
             |    \  ^  
            ---   |  | 
      Gnd --o o---+--+---------> /reset
                  |
                 ===
                  |
                 Gnd           you can use a 10uF cap and a 10K ohms resistor 
                               here 
Legend === capacitor
      /\/  Resistor
     ->|-  diode
      |
     ---   toggle switch
    -o o-