Did you tested the pin with a scope?

And..
Why do you want to do your own downloader?.. My example is to do an IAP not a true downloader.

This toogle bit code will be your downloader or your aplication code?
If is the aplication code:
Why your code starts in 2000h?
Did you set the reset jump?.....
org 0
ljmp 2000h

If is the downloader code:
Why do you set the SBV to FCh
It must point to your downloader test code 20h.
Are you sure than after this downloader code was charged the device is still functional? or you need a parallell programer to re-write the SBV byte?

What is the SBS byte i can't find it in the datasheet?