leonzha

"Netduino uses crystal oscillator ABM7-18.432MHZ-10-D2Y, which according to the datasheet has frequency tolerance ±20 ppm and stability ±30 ppm. " i am try to make own pcb with the netdunio plus schemetic. currently, when i plug the usb onto my computer, it says unknown device. but i can upload the netdunio mini firmware through DBUG pins. i think the problem may causing by the main crystal i used. from at91sam7 datasheet Page615. CL (6) Equivalent Load Capacitance Integrated Load Capacitance (XIN and XOUT in series) 20pF CLEXT (6) Maximum external capacitor on XIN and XOUT 10 pF by using ABM7-18.432MHZ-10-D2Y the External Load Capacitance will be 10*10/(10+10)+ 5pf(inconsideration of track...)=10pf, this seem did not consider internal equivalent load capacitance. i am not using this crystal at moment. why this mcu only allow max of 10pf load capacitance? this is not common on market, unless i order it. hope someone help me to understand this. appreciated