Chip,

The ECU without the add on board for dizzi ignition does have the dwell time in the normal ECU eprom but thsi is very rough and ready as its there purely as a power saver as it relys 100% on the ignition amp doing the bulk of the donkey work as mentioned above.

The add on board analyses this original ignition signal and only needs to know when the plug is needed to fire.
It discards the dwell part of the signal as this is useless to use for the coil pack as each coil would see way too much charge and wasted heat in the coil due to them being energised too long would eventually burn them out if not corrected.