Before you start an operation, the speed and the number of output pulses are set in the registers in LSI.
If the next operation data is set after the operation is completed, a stop time for software processing will occur.
So there is a pre-register to set the operation data for the next operation during the current operation.
The pre-register exists for each function such as operation speed and output pulse number, etc.
When the current operation is completed, the set value of each pre-register is copied to the corresponding register at the same time, so the next operation starts immediately.