No point in calculating or showing, since full compare against desired bits is done at every startup -- way better than a CRC, and if it fails tries to program. If programming fails, the PortaPack panics and LED flashes.
Turns out 0x10088000 - 0x10089fff is not the right place. It's 0x40041000, and is only 256 bytes!
Move PPM to correct place, change representation to PPB for finer control.
Reset PPB value to initial value if read value out of bounds.
Clip PPB value on write to permitted bounds.
Contributes to resolution of issue #11.
