FTDI produce a range of serial devices which utilise the FTDI sio driver in Linux with various capabilities.

This uses an FT8U100AX USB bridge as seen in the foreground of the picture. This chip combines multiple functions which include serial I/O.

This device fails to operates on correctly on a USB 2.0 port and a connection to a USB 1.1 port or hub is essential.

Bus 001 Device 016: ID 0403:8372 Future Technology Devices International, Ltd FT8U100AX Serial Port

Devices as the one in the background of the picture above are generally FT232-RL clones yet they can easily achieve 1 megabaud. 2 megabaud has also been tested but not extensively. They also support the libftdi API in Linux.

Bus 001 Device 019: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC

         USB SOCKET
PWREN                     DCD
TXDEN                     DSR
SLEEP                     GND
CTS                       RI
3.3V                      RXD
5V                        VIO
RXLED      JUMPER         RTS
TXLED      5V-3.3V        DTR
GND                       TXD
    DTR RX TX VCC CTS GND
    
JUMPER SELECTS VIO

This board is manufactured by FTDI as an FT232-RL evaluation kit which has an almost full break-out of the chip pins. The jumpers either select bus power or isolate the device and also allow to selection of either 3V3 or 5V I/O.

Bus 006 Device 002: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC

            UM232R
DB0 TXD  1  J1-123  24 GND 
DB4 DTR#               CB0
DB2 RTS#               CB1
VIO                    VCC
DB1 RXD                RST
DB7 RI#                3V3
GND                    CB3
DB5 DSR#               PU1
DB6 DCD#               PU2
DB3 CTS#               VCC
CB4          J2-21     USB
CB2      12         13 SLD
           USB SOCKET
         
J1
 1-2  VIO = 3V3
 2-3  VIO = VCC (DEFAULT)

J2
 ON   VCC = USB (DEFAULT)
 OFF  VCC = SELF

<code> eeprom_size = 128 vendor_id = 0x0403 product_id = 0x6001 self_powered = 0 remote_wakeup = 1 suspend_pull_downs = 0 max_bus_power = 100 mA manufacturer = FTDI product = UM232R USB ↔ Serial serialnum = FT90IYOQ high_current_io = 0 load_d2xx_driver = 0 txd_inverted = 0 rxd_inverted = 0 rts_inverted = 0 cts_inverted = 0 dtr_inverted = 0 dsr_inverted = 0 dcd_inverted = 0 ri_inverted = 0 cbus[0] = RxLED cbus[1] = TxLED cbus[2] = PwrEn cbus[3] = PwrEn cbus[4] = Sleep </code> <code> eeprom_size = 128 vendor_id = 0x0403 product_id = 0x6001 self_powered = 0 remote_wakeup = 1 suspend_pull_downs = 0 max_bus_power = 90 mA manufacturer = FTDI product = FT232R USB UART serialnum = A50285BI high_current_io = 0 load_d2xx_driver = 0 txd_inverted = 0 rxd_inverted = 0 rts_inverted = 0 cts_inverted = 0 dtr_inverted = 0 dsr_inverted = 0 dcd_inverted = 0 ri_inverted = 0 cbus[0] = TxLED cbus[1] = RxLED cbus[2] = TxDEN cbus[3] = PwrEn cbus[4] = Sleep </code>

FTDI UM232R user guide
libftdi for Linux
Bit-bang mode