Does setting a pin to be TWI SCL or SDA enable its pullup?

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

motlib — Sun, 21 Aug 2016 00:26:17 GMT

In the product specification (version 3.0), you can find in section 28.2 for master mode configuration and also table 258, that you need to configure the pull-up resistors for SDA and SCL in the GPIO peripheral manually. The TWI unit will not do this automatically.

You need to configure the pins, before enabling the TWI, so that there can no glitches occur on these pins, which might confuse the connected TWI slaves.

Perhaps one of your slaves has a tendency to float its pins high, so acting as a weak pullup (BTST...). But this is no reliable communication. Perhaps even attaching a scope disturbs the line levels enough to make communication fail.

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

CurtisHx — Mon, 15 Aug 2016 20:11:18 GMT

Are you talking about the driver source code or the nRF52 Product Specification? Because the product specification does say that you have to manually configure the pins when you turn the MCU off. But I don't care about turning the MCU off. I want to know: Are the internal pull ups automatically enabled when you set an IO as SDA or SCL.

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

Justin — Mon, 15 Aug 2016 20:03:23 GMT

The comment in the Nordic driver implies that they set the gpio conf so that the pins will be in a valid state when the MCU is powered off

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

CurtisHx — Mon, 15 Aug 2016 17:17:59 GMT

Nope. Nothing is explicitly setting the GPIO registers.

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

Justin — Mon, 15 Aug 2016 17:10:45 GMT

to be clear, are you setting NRF_GPIO->PIN_CNF ?

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

CurtisHx — Mon, 15 Aug 2016 11:21:00 GMT

Forgot to note that I'm writing a driver for the I2C module and going directly after the hardware registers.

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

CurtisHx — Mon, 15 Aug 2016 11:20:32 GMT

@milanez No Softdevice. I've been bare-metal programming

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

milanez — Thu, 11 Aug 2016 23:02:36 GMT

Hy, what your softdevice version ?

RE: Does setting a pin to be TWI SCL or SDA enable its pullup?

Justin — Thu, 11 Aug 2016 22:28:28 GMT

If you're using the driver it does enable the pull ups. See nrf_drv_twi.c line 44.