101 USB CDC (Serial)

101 : USB CDC (Serial)

How it works

All the magic happens in https://github.com/davidthings/tinyfpga_bx_usbserial.

How to test

Set the clock frequency to 48 MHz. Connect usb_p and usb_n pins to D+ / D- USB pins through 68 ohm resistors. Pull up D+ with 1.5k resistor.

The device should appear as a serial port on your computer. Data received from USB host will appear on the output pins (rx) when rx_ready goes high. You can send data to the USB device by waiting for tx_ready to go high, setting the input pins (tx) to the byte you’d like to transmit, and setting tx_valid high.


# Input Output Bidirectional
0 tx[0] rx[0] usb_p
1 tx[1] rx[1] usb_n
2 tx[2] rx[2] tx_valid
3 tx[3] rx[3] tx_ready
4 tx[4] rx[4] rx_valid
5 tx[5] rx[5] rx_ready
6 tx[6] rx[6] dp_pu_o
7 tx[7] rx[7] configured