Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

awneil — Fri, 28 Jun 2019 09:09:34 GMT

[quote userid="13562" url="~/f/nordic-q-a/49050/can-i-set-the-nrf51822-spis-miso-pin-as-output-when-there-is-only-one-spi-slave-and-one-spi-master-on-the-bus/195290"]I do not know how I can be any more clear[/quote]

Indeed.

cgha: again, look at the SPI Slave example in the SDK - it will show you how to correctly configure the nRF as an SPI Slave.

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

haakonsh — Fri, 28 Jun 2019 08:57:54 GMT

I agree with awneil, you do not need a pull resistor on an SPI line unless something is seriously wrong.

I do not know how I can be any more clear than:
dir = NRF_GPIO_PIN_DIR_OUTPUT
input = NRF_GPIO_PIN_INPUT_DISCONNECT

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

awneil — Fri, 28 Jun 2019 07:44:07 GMT

And that output will always be driving either high or low - because that's what SPI requires.

SPI is not like I2C - where pullups are required because open-drain outputs are used.

Pull-up/down resistors serve no useful function in SPI - they purely waste power.

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

cgha — Fri, 28 Jun 2019 01:27:30 GMT

@haakonsh do you mean set as input and enable pull down?

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

cgha — Fri, 28 Jun 2019 01:25:59 GMT

nordic sdk set this miso pin as input&no pull when spis is initialized, and when it is selected(cs down), this pin function as miso, otherwise it is set as high impedence, just like other spi device, this is useful when there has more than one spi device on the bus. But in my system, there is only one spi device, So I want to set it as output.

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

awneil — Thu, 27 Jun 2019 14:11:45 GMT

So, surely, it will always be driving - either high or low ?

Therefore a pull up/down is pointless - it will just waste power and serve no useful purpose at all?

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

haakonsh — Thu, 27 Jun 2019 14:06:22 GMT

Oh, right, the miso is already an output, you just need to set the pull configuration.
Use nrf_gpio_cfg:

dir = NRF_GPIO_PIN_DIR_OUTPUT
input = NRF_GPIO_PIN_INPUT_DISCONNECT
pull = NRF_GPIO_PIN_PULLDOWN
drive = NRF_GPIO_PIN_S0S1
sense = NRF_GPIO_PIN_NOSENSE

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

awneil — Thu, 27 Jun 2019 14:05:29 GMT

[quote userid="6959" url="~/f/nordic-q-a/49050/can-i-set-the-nrf51822-spis-miso-pin-as-output-when-there-is-only-one-spi-slave-and-one-spi-master-on-the-bus/195164"] I just want to give the miso pin on slave side an const value[/quote]

But SPI requires a constant drive - either high or low - anyhow.

SPI is not open-drain.

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

cgha — Thu, 27 Jun 2019 13:21:32 GMT

Yes, I just want to give the miso pin on slave side an const value. The new sdk set this pin pull on master side, but my spi master is an otp mcu. I think the pullup or pull down resistor will cost more power in spi transfer, so I want to set this pin as output.

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

haakonsh — Thu, 27 Jun 2019 12:56:40 GMT

Yes, you can set the pull configuration in the PIN_CNF[x] register, but, are you sure that's what you want to do?

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

cgha — Thu, 27 Jun 2019 12:43:59 GMT

So do you mean I can set the intenal pull resistor on spis miso pin?

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

haakonsh — Thu, 27 Jun 2019 11:34:41 GMT

I don't understand what you are trying to achieve by setting the SPIS miso pin as an output.

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

cgha — Thu, 27 Jun 2019 08:11:53 GMT

Thanks for your information, but I think it does not help my question. In the sample code, miso pin has no pull, and this may put miso in float state.

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

awneil — Thu, 27 Jun 2019 08:00:20 GMT

https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v12.3.0/spi_slave_example.html

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

cgha — Thu, 27 Jun 2019 07:54:49 GMT

nrf51822 is spi slave, and the spi master is another 8bit mcu(with miso pin set as input and no pull).

RE: Can I set the nrf51822 spis miso pin as output when there is only one spi slave and one spi master on the bus.

awneil — Thu, 27 Jun 2019 07:43:06 GMT

Is the nRF51822 the slave or the master?

Or is this two nRF51822s connected by SPI - so one is slave, and the other is master?