MAINCLK = 18.432MHz
PLLCLK(div=24,mul=125) = 96MHz
MCLK(divisor 2) = 48MHz
USB(divisor 2) = 48MHz
MC_FWR(FWS) = 2 # 1 flash waitstate
SPCK(SCBR=10) = 4.8MHz # 5MHz max clock RC632