10 Replies Latest reply on Apr 15, 2014 12:21 PM by adroid

    USB to TTL Connection




      i didn't got a serial connection running yet - no output.


      My setup was like in the blog post with the same cable.


      blog post:

      Impressions on the RIoTboard and changing its Operating System in Windows


      Same cable with my raspi works great.


      Do i need to setup something first?



        • Re: USB to TTL Connection

          It should work directly. As soon as you pressed the reset button it should give you some output.


          Maybe you switched the txd with the rxd pin? Then you wouldn´t get any response.

            • Re: Re: USB to TTL Connection

              Thanks for the hint Otto.


              Unfortunately it didn't help. I also tried with 2 different boards - one with factory settings and one with Ubuntu on EMMC.

              No luck




              Cable: TTL-232R-RPi (FTDI-Chip)

              black - GND

              orange - TX

              yellow RX


              Also tried other cables with one of the riot-boards: TTL-232R-3V3, CR-409202


              Do i need to set any jumpers to enable serial interface?

                • Re: USB to TTL Connection

                  No jumpers needed, it should just work right out of the box at 115200 baud 8-N-1, From your photo, I think the red/orange cables should be swapped.


                  Does Android/Linux come up? I just want to make sure the switches on SW1 are in the default position. If you see Android/Linux, you should see output on the terminal.


                  I used this cable with no problems: http://www.embest-tech.com/product/extension-module/uart8000-u.html

                  Riot (J18):                Cable:

                  1  (TXD)                     Green (RXD)

                  2  (RXD)                     Red (TXD)

                  3 (GND)                      Black (GND)


                    • Re: USB to TTL Connection

                      Yes, Android / Linux come up. I also tried to swap rx / tx (yellow and orange in my case), but no success.


                      I will do further testing

                      • Re: USB to TTL Connection

                        Ah, you are right - i switched yellow and orange and it's working


                        Not sure why it didn't last time

                          • Re: Re: USB to TTL Connection



                            right now i don´t have access to that cable, so i figured that i could use a USB to RS232 serial DB9 Adapter instead of the usb to ttl.

                            But i when i connect to the port i get this :


                            Þ¯^}U-û›mªªÊ”ê:ªúk +=Mû›ê*j:jô» uöëºô‹Ö¶ö+½-ZåW/5='¿ 5# ! - /¿ -!¿…¿—ëåÔºT´TZö


                                              ú»êºÔúûöTö¬ªö6ª6Zå% “ ¿ ''‹¿‘›eo

                                                                                ëå% “ ¿ ''›‹¿•›eo

                                                                                                  ëå% “ ¿ ''


                                    ëå% “ ¿ ''‹¿•Ÿeo

                                                     ëå- 1¿9'!9)¿¿¿¿¿‹¿““ŸŸŸŸŸŸo

                                                                                ëå- 1¿ 59'!9)¿‹¿““ŸŸŸŸŸŸo



                                                  ëå9  -¿9'!9)¿¿¿¿‹¿“ŸŸŸŸŸŸŸo




                                                   ëå5%-A '! ¿9'!9)‹¿ŸŸŸŸŸŸo




                                                    ëå  7/9›¿9'!9)¿¿‹¿ŸŸŸŸŸŸo

                                                                                ëå  7/9™¿9'!9)¿¿‹¿ŸŸŸŸŸŸo



                            ëå  7/9—¿9'!9)¿¿‹¿ŸŸŸŸŸŸo



                            ëåw[}e‹¿¿¿¿q{ëå´!=‹¿Ÿ “Ÿ¿I_a[¿Eëå{!! ¿w5 -95‹¿eeyëåm›y‹¿¿¿=7



                            i just can´t get the desire output , my connections are like these:



                            serial DB9              Serial Debug RiotBoard


                            2 - Rx                    1 - Tx

                            3 -Tx                      2 - Rx

                            5 - GND                3 - GND



                            i,m using this port settings on hyperterminal and also with PuTTy


                            115200 baud rate

                            8 bits data

                            1 stop bit

                            no parity

                            no flow control


                            am i wrong using the usb to serial adapter ? it looks to me that i should work the same as the usb to ttl right ?

                              • Re: USB to TTL Connection

                                The port speaks on UART not RS232 so you get that stuff.

                                You´ll need an USB to UART adapter.

                                  • Re: USB to TTL Connection

                                    To clarify, a UART is a Universal Asynchronous Receiver Transmitter. and in most modern versions It is capable of communicating in numerous serial protocols including those commonly used for the  RS232 standard. It is also typically fully implemented within a single chip or even embedded into micro-controllers and micro-processors used in Arduino, Raspberry PI and other popular evaluation boards. they often can also support I2C, SPI and other standards


                                    RS232 is commonly used as a generic term for the whole serial communications but more specifically it refers to the physical and electrical interface. (RS422, RS485 and others are also physical and electrical standards that a UART can support with the correct interface hardware, in many case the actual data protocol is the same travelling across the wire)


                                    see the following links, as you will see they are all variations on a theme.





                                    so to be pedantic, there is no such thing as a USB to UART adapter, It would be more generically correct to say USB to Serial and this would have to also be coupled to the interface configuration aka it would be one of the above or as required here USB to TTL. In all cases a UART is the device off loading the serial communications, the variations are the electrical interfacing and the physical connector configuration.


                                    Hope this helps

                                  • Re: Re: USB to TTL Connection

                                    A USB to Serial (DB9) could easily be also upping the voltage on the pins to be compatible with true serial interfaces, that is anything from +-3V to +-15volts


                                    this would be catastrophic to an interface only tolerant of 0-5V (TTL)


                                    so using a USB to Serial DB9 is probably a very bad idea and one of those "Use at your own risk" items.


                                    If the interface specifically asks for USB to TTL, that's what you should be sure your using or face the consequences of a fried interface.