Help with FTDI (USB->UART) connection

[Jerod]

I purchased a pair of FTDI cables, and I can't seem to get them to work.

Unsure if the pinout is standard but here is the mapping of the cables provided:

Red wire： 5V

Black wire： GND

White wire： RXD

Green wire： TXD

Yellow wire： RTS

Blue wire： CTS

I have mapped these to the proper GPIOs in my board file:

#define RX_PIN_NUMBER GPIO_06 // FTDI_USB_UART_WHITE == RXD

#define TX_PIN_NUMBER GPIO_07 // FTDI_USB_UART_GREEN == TXD

#define CTS_PIN_NUMBER GPIO_30 // FTDI_USB_UART_BLUE == CTS

#define RTS_PIN_NUMBER GPIO_05 // FTDI_USB_UART_YELLOW == RTS

#define HWFC true

and initialized serial comms with:

simple_uart_config(RTS_PIN_NUMBER, TX_PIN_NUMBER, CTS_PIN_NUMBER, RX_PIN_NUMBER, HWFC);

Standard connection that I usually use via the eval-kit's UART-via-SEGGER is 38.4K, N, 8, 1, RTS/CTS, so I've setup the new comm port with these same settings.

Unfortunately, can't get any text (not even garbage) through the comm port.

Windows detects the FTDI and sets up the COMM port correctly, so I don't believe the problem is there.

If USB is plugged in first (prior to board power on), the board may not even boot, as it gets stuck/stops at the serial init line.

I'm concerned that perhaps I have the cable color pins wrong.

Measuring against the black (GND), I get 3.3V on all data wires (Yellow, Blue, Green, White), which I find odd, given that I measure 3V on the RTS pin on the board prior to connecting the cables.

So -- it seems odd that I should get 3.3V on all lines -- but not sure how this all is supposed to work.

Any advice?

[endnode]

Hi Jerod,

I'm using FTDI UART-to-USB cables with Nordic's nRF51 chips on daily basis and it definitely works. However I'm not using HW flow control and I always connect only 3 wires (GND, Tx and Rx). There is usually also catch in Tx/Rx settings because you always need to double check what's the current view (if Tx/Rx colors on the cable correspond to PC view or Nordic;).

If you would be interested into my settings (I'm using mostly only UART Tx from Nordic at higher speeds like 115k or 250k for debug output into console on PC) just let me know.

Cheers Jan

[Jerod]

Thanks Jan -- this was most helpful!

Sometimes just knowing the setup someone else has compiled is sufficient enough.

The thing that fixed this for me is when you said -- which direction is the TX/RX.
I had neglected to remember they were probably from the PC -- and not the Nordic.

The working setup is now:

Using 3 wires: WHITE, GREEN, BLACK White is configured as TX (from Nordic output point of view) Green is configured as RX (from Nordic input point of view) Black is GND

I was able to get this working at both 38400, and 115200 -- Thanks for your help!