I think the 'forced' monitor entry that Alban is speaking of is intended to be used in the factory for programming a brand new blank device that is fixed to a PC board with all of the pins already connected for the intended application. It usually uses only one pin to communicate serially to the programmer and one pin to set the mode. I think the idea is that there will be jumpers on the PC board or pullup/down resistors to set the mode when the device is being programmed and after that it will go into user mode since the startup vector will no longer be blank. There is another way to go into the monitor mode when the device has already been programmed, but you have to use a specific clock, and there are more pins that get used to tell the monitor software what type of clock is being supplied, whether to disable the COP, etc.
When I program the HC08 devices, I usually comment out the startup vector in the .prm file so that I can use more of the pins for debugging. Then when I think I have everything just right, I'll uncomment the startup vector and do a final test in user mode. If I need to change something after that, I'll put the microcontroller into a separate board with the extra pins already set to go into monitor mode and then I'll erase the flash back to all 0xFF - which then makes it work again in the original setup, just as if the microcontroller is brand new. The BDM setup on the HC(S)12 and the HCS08 devices is far superior, but the HC08 DIP devices are handy if you want to build things on a breadboard and you don't want to buy/build a development board.
