erik malund wrote:
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If you had included the code exactly as described in backdoor.doc on my home page, you would not have problems.



again, this can not be done after the fact it has to be included before you need to rescue the chip.



Erik



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Well well well,
this is how I did it and hoped it would work...
This was my sample program that worked PERFECTLY well with Atmel 89C51 (programmed via a prallel programmer) but the same problem... (gets programmed the first time but refuses to get detected later).

<code>
org 0
; the following lines are added for protecting the security bits of Philips Chip
; omit/comment the next line if you are using ATMEL chip.
ajmp bootck
ajmp main ; will not run if the above line is not commented

org 50h
bootck:
jb P3.1,main ;TxD always high without cliplead
mov AUXR1,#020h ;enable boot
;!!insert parametres for set boot vector as in AN 461 pg 14
call 0fff0h
;!! insert parametres for set status byte as in AN 461 pg 14
call 0fff0h
jmp $ ;wait for reset

org 70h
main:
mov p0,#0
mov p1,#0
mov p2,#0
mov p3,#0
begin:
mov p1,#0ffh
acall wait
mov a,p1
cpl a
mov p1,a
sjmp begin

wait:
mov r0,#0ffh
l2:
mov r1,#0ffh
l1:
mov r2,#0ffh
djnz r2,$
djnz r1,l1
djnz r0,l2
ret
</code>

And my circuit should be correct, because the first time I program a new/fresh chip, it does get programmed and runs the program.

Regards,
Harsha