Reusing PGC & PGD pins

[richard]

if your re has the possibility that it can be stationary with either A B contact closed [ground] then it will always be possible to stuff up programming and no isolation other than disconnection will work

the isolation objective is
1 don't impose a logic level on the pgm pins that will damage the programmer
2 don't impose a load on the pgm pins that will corrupt the programming signals
3 allow your signal to reach the pins without signal corruption