Add info about default gpio drive mode

[microbit-carlos]

As discussed in the Slack channel, we don't provide information about what is the default drive mode for the pins (high drive @5ma or normal @0.5mA).

Would this be the best place to put it? Not sure: https://tech.microbit.org/hardware/edgeconnector_ds/
Maybe it should go to https://lancaster-university.github.io/ ?

[DavidWhaleMEF]

That page on tech is the best page, as it lists pin currents there already (and hints at high-drive). Although at the time we both wrote that page, @jaustin hadn't dug into the mbed code and we were not sure how it was configured, so we left it a bit vague. It would be good for someone to re-verify how pin modes are configured (stddrive or highdrive) and correctly document here.

Also, we have a document from a community member where they loaded up GPIO pins with decreasing resistor values and characterised the pin-voltage-derating that was described to us when I asked the question of nordic.

An engineer at nordic, at that time, ran code in a debugger and set a breakpoint and then inspected the pindrive registers, and confirmed to us that as of then (about early 2017) the pins were all in stddrive (0.5ma) mode. It might have changed since.

[microbit-carlos]

Thanks David, so we still have an action left to double check if the Mbed default configuration is low drive. Once that's done we should update the docs here.