AM572x UART3 TX seems inverted

Hein Thet Aung

Other Parts Discussed in Thread: AM5726

We are working on our custom board using AM5726. It is nearly identical to GP EVM but UART3_TXD & UART3_RXD Pads are being routed as UART3 debug output.

We are trying to redirect UART3 Module to UART3_TXD & UART3_RXD pads, default was attached to UART2_RSTN & UART2_CTSN pads.

I change these in the dts file.

uart3_pins_default: uart3_pins_default {
       pinctrl-single,pins = <
           0x248 (PIN_INPUT_SLEW | MUX_MODE0) /* uart3_rxd */
           0x24c (PIN_INPUT_SLEW | MUX_MODE0) /* uart3_txd */
       >;
};

&uart3 {
   status = "okay";
   interrupts-extended = <&crossbar_mpu GIC_SPI 69 IRQ_TYPE_LEVEL_HIGH>,
                  <&dra7_pmx_core 0x248>;

   pinctrl-names = "default";
   pinctrl-0 = <&uart3_pins_default>;
};

And these in the mux_data.h file

//{UART3_RXD, (M11 | PIN_INPUT_PULLDOWN)}, /* uart3_rxd.pr1_mii0_rxdv */
//{UART3_TXD, (M11 | PIN_INPUT_PULLDOWN)}, /* uart3_txd.rp1_mii_mr0_clk */

{UART3_RXD, (M0 | PIN_INPUT_PULLUP)}, /* uart3_rxd.uart3_rxd */
{UART3_TXD, (M0 | PIN_INPUT_PULLUP)}, /* uart3_txd.uart3_txd */

//{UART2_CTSN, (M2 | PIN_INPUT_SLEW)}, /* uart2_ctsn.uart3_rxd */
//{UART2_RTSN, (M1 | PIN_INPUT_SLEW)}, /* uart2_rtsn.uart3_txd */

Attached image is what we get. TXD pin should be always high but what I get is always low. Looks like it is inverted. In terminal, it is showing weird characters.

I have tested the TXD signal on GP EVM and it is ok. Logic analyzer settings are correct.

Could you advise me what happened?

Regards,
Hein

over 8 years ago

0 Biser Gatchev-XID over 8 years ago

TI__Guru**** 393215 points

Hi,

Why is the TXD pin configured as input with pulldown? It should be output with pullup. Please check that the pinmux is not overwritten by another device tree entry.

0 Hein Thet Aung over 8 years ago in reply to Biser Gatchev-XID

Intellectual 280 points

Hi Biser,

Lines with pulldown config are commented, it is just to show how I made changes.
However, I have also tried output with pull up but not working.

Could you tell me which files to check regarding your answer: "overwritten by another device tree entry"?

0 Hein Thet Aung over 8 years ago in reply to Biser Gatchev-XID

Intellectual 280 points

Hi Biser,

Why the default TXD on UART2_RTSN pad is configured as input?

Regards,
Hein

0 Biser Gatchev-XID over 8 years ago in reply to Hein Thet Aung

TI__Guru**** 393215 points

I have asked the software team to look at this. They will respond here.

0 Hein Thet Aung over 8 years ago in reply to Biser Gatchev-XID

Intellectual 280 points

Hi Biser,

Thank you for your help.

Regards,
Hein

0 Yordan Kovachev over 8 years ago

TI__Guru**** 161600 points

Hi Hein,

You're referring to the core_padconf_array_essential_x15[] structure, right?

You should configure the uart3_txd & uart3_rxd pads, the same way when they were mapped to uart2_ctsn/rtsn pins:
{UART3_RXD, (M14 | PIN_INPUT_SLEW)}, /* uart3_rxd.gpio5_18 */
{UART3_TXD, (M14 | PIN_INPUT_SLEW)}, /* uart3_txd.gpio5_19 */

Also when you refer to the dts file, is this the arch/arm/dts/am57xx-beagle-x15.dts file from u-boot?
Try adding the same configuration (settings) in your kernel .dts file.

In terminal, it is showing weird characters.

Check your terminal settings. They should be as follows:
BaudRate: 115200
DataBits: 8
StopBits: 1
Parity: N

Best Regards,
Yordan

0 Hein Thet Aung over 8 years ago in reply to Yordan Kovachev

Intellectual 280 points

Hi Yordan,

Yes, I am referring to core_padconf_array_essential_x15[] structure and I am booting from arch/arm/dts/am57xx-beagle-x15.dts

I want to redirect UART3 module to UART3_TXD & UART3_RXD pads.

Shouldn't it be Mux Mode 0?
UART3_TXD, (M14 | PIN_INPUT_SLEW) is GPIO output. Isn't it?

I saw weird character because the signal is as shown in the image. It is inverted. Terminal settings are correct, I can see debug message if I use UART2_RSTN pad.

Regards,
Hein

0 Yordan Kovachev over 8 years ago in reply to Hein Thet Aung

TI__Guru**** 161600 points

Hi Hein,

Shouldn't it be Mux Mode 0?
UART3_TXD, (M14 | PIN_INPUT_SLEW) is GPIO output. Isn't it?

Yes, you're right it should be M0.

Can you test with adding PIN_INPUT_PULLUP in the dts file? What is the result?

Best Regards,
Yordan

0 Hein Thet Aung over 8 years ago in reply to Yordan Kovachev

Intellectual 280 points

Hi Yordan,

When I test with UART3_TXD, (M0 | PIN_INPUT_SLEW), no output.

When I test with UART3_TXD, (M0 | PIN_INPUT_PULLUP), still no output.

When I test UART3_TXD, (M0 | PIN_INPUT_PULLUP) together with UART3_RXD, (M0 | PIN_INPUT_PULLUP), gives me output on UART3_TXD pad but the output is normally low, it does toggle. I think it is being inverted.

Regards,
Hein

0 Biser Gatchev-XID over 8 years ago in reply to Hein Thet Aung

TI__Guru**** 393215 points

Which are the physical pins you are using?

0 Hein Thet Aung over 8 years ago in reply to Biser Gatchev-XID

Intellectual 280 points

Hi Biser/Yordan,

I apologize for being troublesome. I found the problem.

Tri-state buffer I am using as in the EVM is causing the inverted output.

Please see my schematic below. I don't know why TX pin gets inverted. I need to check the sample part from distributor.

Regards,
Hein

Processors

Processors forum

AM572x UART3 TX seems inverted