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@Mark_M
Hi fanoush,
to be honest, I do not know. I always thought that the higher frequency the more power a device needs. If it is not a case, then why by default the AT6558 is set to 9600 baud, though it can be set up to 115200? The wire between AT6558 and NRF52 is very short, so why not to set baud rate to 115200?
I have not found specs regarding power consumption for different baud rates. Do you have that? Or I will need to try. But it will not be reliable coz I will measure only time of battery discharge.
Here is interesting idea to disable RX pin at NRF52 https://devzone.nordicsemi.com/f/nordic-q-a/66914/uart-current-consumption. But I doubt that will work for our application, because AT6558 sends data to RX, am I right?
Here in https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fchapters%2Fcurrent_consumption%2Fdoc%2Ffrontpage.html in UART electrical specs there is note "1. High baud rates may require GPIOs to be set as High Drive, see GPIO for more details." , high drive is 14mA there.
Anyway, if 9600 is ok, we can use it. If higher rates will not cause overconsumption, we can also use it.
But still, I need a reliable way to set baud rates. :)
Also I did not want to change BR during functioning, only at beginning of app, i.e. the app reads its usage profile where it will be stated the required baud rate. Then it will run with that.