NOTE:
nothing here will work after the fact, this MUST be done before you lose the bootvector.

The page numbers refer to AN461 2002 jun 24.

I have been promoting NoTouch programming of the Philips P89C.. chips and still do. I realize that I have seen this from the perspective of someone that has a Parrallel programmer as a backup and thus may not have been much help to the amateurs.

The NoTouch should still be included as described in my article for regular program maintenance; however, to be able to rescue the chip when a mistake in the just uploaded code does not allow the program to get to the NoTouch upload and emergency exit should be provided. This "emergency exit" also allow you to lose the boot vector and still provide ISP.

To provide this "emergency exit" include the following the very first time you boot, after that you can forget about bootvectors and the other stuff

where your program looks like 
org 0
ljmp xxxyyy
...

xxxyyy:

change to
org 0
ljmp bootck

bootck:
jb  P3.1,xxxyyy ;TxD always high without cliplead
     mov  AUXR1,#020h  ;enable boot
parametres for set boot vector as in AN 461 pg 14
     call 0fff0h
parametres for set status byte as in AN 461 pg 14 
     call 0fff0h
     jmp  $            ;wait for reset
xxxyyy:   as in your original code

Now when emergency strikes, just use a cliplead to hold TxD to ground, reset, remove the
cliplead, reset again and you are booting.


Have fun,

Erik