Hi,
If you look in MC68HC908SR12/D, Table 10-1, there is all the possibilities to enter the Monitor mode.
If you call the top row "0", the next "1" etc, then the real useful ones are "1" and "2".
"3" and "4" will only work on erased Flash EPROMs (where the reset vector is erased.)
The "3" and "4" are useful for burning HC908SR12 for production. Actually an HC908SR12 with a blank Flash EPROM inside, with a 32 kHz crystal connected, will automatically start in "3". So it will automatically wait for a program to be downloaded.
Note that once the HC908SR12 has been programmed, it will not enter this mode until the Flash EPROM has been erased in another mode.
So I would concentrate on "1" and "2".
The difference between "1" and "2", is how PTC1 is connected and that sets the frequency of the oscillator.
Notice that if you have a frequency of 32 kHz or 4.9152 Mz, you can use an external crystal.
If you want to use the 9.8305 frequency, it must be an oscillator.
Notice also that the PTA0 pin must be pulled high when the /RST pin goes high. So add a 10 kOhm pullup resistor to this pin.
The Vpp voltage must also be present when the /RST pin goes high. The high voltage is not used for the Flash EPROM programming, it selects the Monitor mode.
Yep, I think that was all.
Regards,
Ake