Not a piggy back unit.It's stand alone. The Motoola prosessor has a bus speed of 8 meg,not like most that quote the xtal frequency witch is devided by 4 to get the real bus freq. It has 64 point VE table ( not 8),and is writen in Direct assenbly code which will be good to 16,000 rpm. It will drive suplimentary relay control to 500ma.