I'm trying to create a device that will control a few independent RS485 lines using single USB port.
My first idea was to use GL850G usb hub controller (4 downstream ports), 4x FT232R, 4x MAX485. I had to provide 12MHz clock source for both hub controller and FT232R.
- Should all those devices use single clock source? Why? Why not?
I started my design with common universal clock generator (sg-51 at 12MHz), but FT232R requires 5V level on clock input while GL850G requires 3.3V
So maybe there is a way to shift 5V clock source to 3.3V?
If not - should I:
- use crystal for GL850G and common clock generator for FT232R
- use five independent crystal oscilators
- use crystal for GL850G and internal oscilator for FT232R
What are disadvantages of using internal oscilator?
If stability not cost is the key - how should I do it?