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

[Paul]

If the manual says open collector, then you better put a NPN transistor such as 3904 or 8050 there.

If M95 internally pulled high to +5V, then it is there will be a current (small through) flowing through the nRF internal clamping diode.

If you really want to do your "trick". 51822 IO can be configured as input without No Pulls, which is floating. Then configure it to output and set to 0.

I hope this helps.