I am re-designing a device built around an M16C CPU, to use an RX111 to take advantage of its integrated USB interface. Now I have two doubts. The first is that I didn't find any example schematic or reference about this subject; I laid down my schematic, but I am not really sure that it is correct because I see several pins related to USB, but I connected only two (USB0_DM and USB0_DP). In the old schematic, which uses an FTDI usb-to-serial, there was at least one more connection used to reset the USB bus, and I think this would necessary too for the RX11 but I don't know how to do it.
The second doubt is about the clocking options. Is it possible to use the internal high-speed oscillator, and no external crystal, and have a working USB? I've read that the clock precision / tolerance for low speed USB is 1.5%; given that the internal high speed oscillator is rated at 1% precision, it should work - or am I missing something?
Thank you for help.
Thank you Frank. Reading further the RX111 manual, I discovered that the MCU has already two pull- up/down resistors inside, connected to the D+ and D- lines. So I suppose I don't need to put them in my circuit. But this is not well explained. In my old circuit, using FTDI converter, the manual clearly explained how and where to put that resistor; its function is to signal the USB line in order to make the host detect the slave device. Here with RX111 must be the same, but it already contains the required resistor. OK. About the clocking options, did you actually tried HOCO in this situation? 1% tolerance is fine for "full" speed, but not for "high" speed, I believe. Anyway, I laid down the PCB with "main oscillator" circuitry; if not needed, I will not mount the resonator. Have a nice day, best regards,
Linuxfan