Win APIs                RS232                 USB                UART
SetCommState()       - Setting parameters   - Endpoint 0       - command register
EscapeCommFunction()   (baud, data bits..)                       status register
SetCommBreak()         DTR, RTS
ClearCommBreak()

GetCommState()       - DSR, DCD, RI         - interrupt IN EP  - status register
ClearCommError()       Break status
GetCommModemStatus()   Parity error
                       Frame error
                       Overrun error
                   
WriteFile()          - TX                   - bulk OUT EP      - UART TX

ReadFile()           - RX                   - bulk IN EP       - UART RX

 Host application <--> Device driver <-----> USB hardware <--> Firmware