TriggSpeed and TCP Velocity system output

TriggSpeed instruction allows for generating an analog output voltage proportional TCP velocity. Does anyone know how the analog output voltage is generated internally? From Signal analyzer online, I can see analog output tracking the TCP velocity even during acceleration and deceleration phases. I am just curious as to how this is implemented internally in the controller. Can anybody familiar with the internals of IRC5 controller explain this or point me to a document?