nrf51822 GPIO as open collector driver

[Jose Xavier]

I need to drive low a IO from a GSM modem:

They suggested to this with a open collector driver. On other microcontrollers usually I have a floating option for the IO, so I can have the IO on a floating state and than drive it low. How can I achieve it with the nrf51822 GPIO? I didn't get well the drive options on the reference manual. What standard, high drive and disconnect means and why there are two parameters? Do you have a schematic that could explain it better?

thank you

[Charles Manning]

According to the ref manual, nRF51822s have open collector mode.

In the pin's PINCTL register, set the pin drive to S0D1 "standard 0, disconnect 1". I would expect that's what you want.

Be mindful of voltages though..... You might need an external transistor/FET/etc to buffer the micro.