Problem using three UART ports in nRF5340 (nRF Connect SDK)

[Sukriti]

According to this discussion, all the 4 UARTs are functional in nRF5340. I intend to use multiple UART ports, and I modified this exercise solution to do so. I was able to use UART0 and UART1 for printing to the serial terminal. The pins for UART0 and UART1 have already been defined in the nrf5340_cpuapp_common-pinctrl.dtsi file as:

UART0: 

Tx: 20, Rx: 22

UART1: 

Tx: 1, Rx: 0

However, no pins have been defined for UART2 and UART3. In order to use UART1 and UART2 (in addition to UART0), I made the following changes:

1. Added the following to nrf5340_cpuapp_common-pinctrl.dtsi:

	uart2_default: uart2_default {
		group1 {
			psels = <NRF_PSEL(UART_TX, 2, 26)>;
		};
		group2 {
			psels = <NRF_PSEL(UART_RX, 2, 27)>;
			bias-pull-up;
		};
	};

	uart2_sleep: uart2_sleep {
		group1 {
			psels = <NRF_PSEL(UART_TX, 2, 26)>,
				<NRF_PSEL(UART_RX, 2, 27)>;
			low-power-enable;
		};
	}; 

2. Added the following to nrf5340_cpuapp_common.dts:

//Added later
 &uart1 {
	status = "okay";
	current-speed = <115200>;
	pinctrl-0 = <&uart1_default>;
	pinctrl-1 = <&uart1_sleep>;
	pinctrl-names = "default", "sleep";
};

//Added later
 &uart2 {
	status = "okay";
	current-speed = <115200>;
	pinctrl-0 = <&uart2_default>;
	pinctrl-1 = <&uart2_sleep>;
	pinctrl-names = "default", "sleep";
}; 

The code runs fine with UART0 and UART1. With UART2, the code builds, but nothing gets printed to the terminal.

Question-1: Is the pin assignment for UART2 correct? 

Question-2: Will UART2 by default be used with J-link (which seems to be the case with UART0 and UART1)?

Question-3: If I need to connect an external module through UART1, shall I have to change the default pin assignment?

Question-4: The nRF5340 Hardware documentation states that

           For nRF5340 DK v1.0.0, a third virtual COM port routed to the P24 connector of the DK is supported. The pins are labeled RxD, TxD, CTS, and RTS.

Is UART2 using the third virtual COM Port? If yes, how do I define these four pins stated above in my code? (I can see them on the board)

(I just starting exploring UART around a day ago and hence apologize if the doubts are too basic!)

Thanks

Sukriti

[Kazi Afroza Sultana]

Hello Sukriti,

The UART pin you are using is not routed to any virtual com port (https://infocenter.nordicsemi.com/topic/ug_nrf5340_dk/UG/dk/vir_com_port.html). I also think you should add RTS and CTS pin for flow control. You can try to check these issues.

I will give you answers of the rest of the questions on Monday.

Thanks.

Best Regards,

Kazi Afroza Sultana

[Sukriti]

Hi Kazi!

Kazi Afroza Sultana said:

I also think you should add RTS and CTS pin for flow control. You can try to check these issues

Thanks, I'll add them.

Kazi Afroza Sultana said:

The UART pin you are using is not routed to any virtual com port

I get this. But these ports are already used for UART0 and UART1. What would be the pin assignment if I wish to use all the 4 UART ports? There are no pins defined for them.

I can see, there's a third virtual COM port as well, but how do I use this? The pins are labeled RxD, TxD, RTS and CTS. I can't see any associated pin number. 

Kazi Afroza Sultana said:

I will give you answers of the rest of the questions on Monday.

Sure, looking forward to your response.

[Kazi Afroza Sultana]

Hello Sukriti,

According to https://infocenter.nordicsemi.com/topic/ug_nrf5340_dk/UG/dk/if_mcu.html?cp=3_0_4_2 the nRF53 DK exposes two virtual COM ports.

You can see in the device tree the default UART is uart0 and uart1. However it can also be uart1 or uart2. As per this, I think its not possible to get output from more than two uart instances.

For the first virtual COM port, TX is P0.20 and RX is P0.22. For the second RX is P1.00 and TX is P1.01.

So as you can see, by default UART0 will output on the first virtual COM port and UART1 will output on the second port

https://github.com/nrfconnect/sdk-zephyr/blob/98bc3a7a6b3917ce5a058e7a7271d3036edffb88/boards/arm/nrf5340dk_nrf5340/nrf5340_cpuapp_common-pinctrl.dtsi#L24-L25

https://github.com/nrfconnect/sdk-zephyr/blob/98bc3a7a6b3917ce5a058e7a7271d3036edffb88/boards/arm/nrf5340dk_nrf5340/nrf5340_cpuapp_common-pinctrl.dtsi#L85-L90

One thing I suggested in my earlier reply adding CTS and RTS for flow control. I have looked this issue again and asked our team. It is not required to connect CTS and RTS. Just you have to make sure from the serial terminal that the receiving end does not enable flow control.  

if you want to get output from more than two UART instances, you can use a USB to UART cable .

Thanks. 

BR

Kazi

[Sukriti]

Kazi Afroza Sultana said:

According to https://infocenter.nordicsemi.com/topic/ug_nrf5340_dk/UG/dk/if_mcu.html?cp=3_0_4_2 the nRF53 DK exposes two virtual COM ports

Thanks Afroza, you're right. I had checked this link. I have a few more queries.

A note provided on the same link (Virtual COM Ports) also states that

For nRF5340 DK v1.0.0, a third virtual COM port routed to the P24 connector of the DK is supported. The pins are labeled RxD, TxD, CTS, and RTS.

Can you please help me understand this? I can see P24 connector on my board, and these four pins also (the pins have these labels, and I can't see any pin number associated with them). Can I use this third COM Port? If yes, how should the pin assignment be done in the Device Tree?

Secondly, if I wish to interface an external device on a uart port (say uart0), shall I have to change the default pins already assigned to them? As per my understanding, the default pins can only be used for the serial terminal. Am I right?

Thanks

Sukriti

[Kazi Afroza Sultana]

Hello Sukriti,

As it is shown in the device tree that UART0 pins are default connected to interface MCU, so unless you cut the solder bridge with that, you need to select some other GPIOs pin those are accessible to nRF5340 DK.

''For nRF5340 DK v1.0.0, a third virtual COM port routed to the P24 connector of the DK is supported. The pins are labeled RxD, TxD, CTS, and RTS.

Can you please help me understand this? I can see P24 connector on my board, and these four pins also (the pins have these labels, and I can't see any pin number associated with them). Can I use this third COM Port? If yes, how should the pin assignment be done in the Device Tree?''

You can check this here https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.1.0/nrf/ug_nrf5340.html#nrf5340-dk-v1-0-0-com-ports 

Thanks.

BR

Kazi