How to set GPIO as open drain ouput mode

RE: How to set GPIO as open drain ouput mode

Jack-h — Tue, 14 Mar 2017 02:40:09 GMT

Hi,why I configured this like you,but my ds18b20 also be invalid?

RE: How to set GPIO as open drain ouput mode

JiachengWang — Tue, 25 Nov 2014 21:13:41 GMT

Its my mistake. The pin is connected to LED, some voltage go to LED, after changed the pin, I got 3.3v output. Yes, the pin can be written as 1 or 0. However, when I try to read the pin, it is always 0 even the pin is HIGH state, so I change the above code with "GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos", that I can read 1 or 0. Does this change make sene ? Thanks.

RE: How to set GPIO as open drain ouput mode

Stefan Birnir Sverrisson — Tue, 25 Nov 2014 14:07:11 GMT

That sounds strange. What resistor value are you using?

RE: How to set GPIO as open drain ouput mode

JiachengWang — Mon, 24 Nov 2014 15:35:45 GMT

Thanks. However, the output voltage is only about 2.0v when write 1 to the pin, no matter the pin is pulled up to 3.3v or 5.0v. How to get 3.3v output? Thanks again

RE: How to set GPIO as open drain ouput mode

Stefan Birnir Sverrisson — Mon, 24 Nov 2014 14:04:18 GMT

If you intend to control a GPIO pin signal with a connected external pullup resistor with a scenario like in the image bolow

then you can configure the pin in the following manner:

	NRF_GPIO->PIN_CNF[pin_number] = (GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos)		
                                  | (GPIO_PIN_CNF_DRIVE_S0D1 << GPIO_PIN_CNF_DRIVE_Pos)
				  				  | (GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos)
								  | (GPIO_PIN_CNF_INPUT_Disconnect << GPIO_PIN_CNF_INPUT_Pos)
								  | (GPIO_PIN_CNF_DIR_Output << GPIO_PIN_CNF_DIR_Pos);

then when you write 0 to the pin, it will drive it to low signal with drive strength of 0.5mA max (standard drive strength). If you write 1 to the pin, it will be disconnected and the external pullup resistor will drive the pin to high signal.

If you change the configuration to

(GPIO_PIN_CNF_DRIVE_H0D1 << GPIO_PIN_CNF_DRIVE_Pos)

then the pin will be driven to low signal with max 5mA current (high drive strength) when you write 0 to it. When you write 1 it will be disconnected.

Update 25.11.2014 You can use this example directly to test this, just replace the LED configuration line with the configuration code listed above, then you should be able to set pin p0.08 pin by pressing button 0 and clear pin p0.08 with pressing button 1. Remember to change the configuration of the example if necessary so that it fits to your development/evaluation kit, see this thread