How to get more than 2 UART's

[zazas321]

From the nRF52840 specification it seems that the CPU only has 2 UART peripherals. For my particular project, I need to have atleast 4 UART peripherals:

1. UART0 - for logging and debugging

2. UART1 - For communicating with LTE modem

3. UART2 - For communicating with the GNSS

4. UART3 - For communicating with the CO2 sensor

I would like to know what are the most optimal solutions if we need to use more than 2 UART on the nRF52840?

[nordicator_prim3]

You could save one UART by using the USB peripheral for logging and debugging if that fits your needs.

There may be a better solution, but on our custom board we ended up using a 4-channel CMOS switch chip (like this). The GNSS likely needs to always be communicating with the host, but the LTE and C02 could likely share a UART via something like the chip mentioned above. Basically you would just have a GPIO pin to the switch that determines which device that UART is talking to at any given time.

Alternatively, you could use USB for debug/logging and find a C02 sensor that uses i2c/spi instead of UART. Then your LTE and GNSS would have their own UART.

[zazas321]

I guess that is one way to achieve this for my particular application.  But I am really curious to know if there is a way to configure additional software UART 's to use with any 2 spare GPIO's?

[Kenneth]

Hello,

You may consider using the nRF5340 that have 4 UARTs ref;
https://infocenter.nordicsemi.com/topic/ps_nrf5340/uarte.html#topic 

For the nRF52840 you can save 1 UART by for instance using RTT for logging (over SWD interface).

If you choose to use the nRF9160 as LTE modem you can also save 1 UART, since the nRF9160 have a GNSS built-in, ref;
https://infocenter.nordicsemi.com/topic/ps_nrf9160/gps.html 

You can likely also save 1 UART by using a CO2 sensor that have SPI or I2C interface instead of UART.

Kenneth

[zazas321]

Thanks for the reply. I understand that there are many workarrounds when it comes to this particular example.

But I want to know if there is a possibility to create more UART's on the nRF52840 in software? Would there be any limitations or drawbacks? 

Lets assume that the custom PCB has already been designed and there is no option to choose any other method but to configure the UART on spare GPIO's

[Kenneth]

I do believe bit banging UART is possible, but it will only be possible for slow UART communication and increase current consumption since the CPU will be running most of the time. Not recommended and not something I have looked into in specific.

Kenneth