Unable to get UART4 working on FRDM-K64F

[dave408]

I'm using a FRDM-K64F with a handful of peripherals.  At the moment, I cannot get UART4 to work.  I have PEx set up to use PTE24 and PTE25:

I'm using the same settings (with the exception of pins) for UART3 for an RS485 transceiver, and it works just fine.  But when I look at the output of TX on the scope, I get nothing.

Can anyone suggest something that I might be doing wrong?  Here's what I have done so far:

• Double-checked the PEx auto-generated code and it looks correct.  Pin muxing is set properly for HW_UART4.  UART_DRV_Init() is called from Components_Init().
• Stepped into the call to UART_DRV_SendDataBlocking for my RS485 and my UART4 code, and they follow the same path and supposedly send similar type of data, except that UART4 doesn't do anything on the pins.

[DavidS · Accepted solution]

Hi David,

I have UART4 successfully working on PTC14/15 of FRDM-K64F Freedom board.

Looking at Freedom schematic the PTE24/25 connect to FXOS8700CQ pins 4/6 that also have 4.7k pull-ups that might be messing with you.

My simple test was hardwiring PTC14/15 at J199 pins 3-4 for a hardware echo test.

Regards,

David

[dave408]

Thanks, David, as usual you were spot-on.  I should have remembered that there were other I2C peripherals on the FRDM.  I never use them and had completely forgotten.:smileysilly:  I guess the settings were correct since I hooked up the peripheral and it immediately responded to my serial command once I moved over to PTC14/15.

[dave408]

On another note, did my PEx configuration look reasonable enough to you?

[DavidS]

Yes.

My setup was close but I was using interrupts with callbacks only because another customer wanted to see that work.

Note the Bluetooth is just a name.

Regards,

David

[dave408]

Yup, I know the port is general purpose and not just for BT, much like the one that's there for the nordic RF breakout board.  I have to play with callbacks later -- at the moment I'm using a thread that waits forever for incoming data to arrive on the Rx pin.  If you have comments about the downside of such an implementation, I'd love to hear your thoughts.

[dave408]

Thanks for the tip, David!  I hadn't considered that, or the Bluetooth header you used for your test.  I'll give that a try.