Using UART3_TXD (GPIO3[24]) as an GPIO

[yonatanzvi]

I'm using Variscite SOM-SOLO.

I cannot use UART3_TXD (GPIO3[24]) as an GPIO.

I can do that on UART2_TXD (GPIO3[26].

What could be the problem?

[josephzhou1]

see

[igorpadykov]

Hi Yonatan

seems on that board UART3 is used in DTE mode,

that is UART3_TXD is input and connected to output

U25 SN74AVC4T245 . Suggest to post that on

http://variwiki.com/index.php?title=Main_Page

Best regards

igor

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[yonatanzvi]

Dear Igor,

As I understand, if we didn't change the DCEDTE control bit, it should be set as DCE (0), by default. No? So, actually, UART3_TXD had to act as an output. The pin is indeed acts as an output, it constantly set to 3.3V.

I also checked the RTS and CTE pins, to verify if we are in DCE or DTE mode. Seems that CTS acts as an output, which means we are in a DCE mode, no?

We also tried to modify the DCEDTE control bit, but seems that we have no control. CTS remained as an output, while RTS remained as an input.

Looks like something else is overruling our control.

[igorpadykov]

Hi Yonatan

problem is that output U25 SN74AVC4T245 is

connected to UART3 UART3_TXD, so whatever

mode you choses U25 will drive that signal, not UART.

~igor

[yonatanzvi]

Dear Igor,

Okay. So I understand I cannot do nothing with this signal.

I have to look for another alternatives, like CSI0_DAT14 (GPIO6[0]), to get my desired GPIO.

Many thanks for your support and prompt reply.

Yonatan