Now, comes the tricky part with FlowCode.
We just bought the last version of FlowCode 6. It has the screen a bit different compared with FlowCode 5, which I previously used. The meanings of parameters are the same only the windows are a bit different.
In the past I made the mistake by confusing the parameter Clock speed with the crystal frequency.
Now I see that the crystal frequency (marked A) is not directly mentioned in FlowCode in this case. It is only mentioned through parameter OSC Select (marked B) when we have to choose the input frequency of the crystal in order to divide the crystal frequency with PLLDIV in order to get always 4MHz at input of PLL.
Later, the bit FSEN has to be set for full USB speed 48MHz.