Actually the MCU itself has a resistor ( minimum 50k Ohm) pulling down the RST pin. So if you really want to keep it very simple then a 10 micro Farad capacitor to Vcc is all you need for reset.

And your problem could be that you are not vectoring the Start to 0H. When reset, the MCU goes to the code location 0H looking for code to execute. If nothing is there, it kind of goes crazy and crashes.

1. With most assemblers, this is all the code you require :

  CSEG
  
  ORG   0000H
  JMP START

  ORG   0030H     ; Safely jump over  all interrupt vectors

  START:  MOV P0, #0FH
          MOV P1, #0FH
          JMP     START

  END

2. Would be a good idea to see if the ALE pulses are there with a scope.

3. How sure are you that the Flash is programmed ? Did you try to read it back or enable verify during flashing ?

That little guy with 40 shiny legs is a mean fellow and will try all tricks in the world to confuse you, if he knows you are starting fresh.. don't let him have his way.

raghu

Raghu