SPI doesn't stop after sending one Byte

[developer1.0]

Hey Guys,

I have used the basic SPI Example from the nordic website, where a SPI Master is configured and a Text can be sent via SPI.

I used this code to send only one byte (the letter 'T') via the MOSI lane (i need it to send one byte later for in a  project).

My Hardware is the Nordic evaluation board PCA10040 V1.2.1.

I have used default configuration for the SPI like in the example. When i execute the following code and m_length is 1, then the SPI transfers 2 Bytes instead of one, while the second byte is 0xFF.

nrf_drv_spi_transfer(&spi, m_tx_buf, m_length, m_rx_buf, m_length);

The decoded waveform is shown in the picture below. My problem is the second byte, where the MOSI Lane is always high.

I only want to send the first byte. I have no idea, why the clock doesn't stop after the first byte. Can Anybody help me out, with this problem?

Thank you very much :)

[Jørgen Holmefjord]

Hi,

This is in the errata. Since you call nrf_drv_spi_transfer with the last parameter set to m_length, you are also trying to receive one byte. If you set the last parameter to 0, you should be able to transmitt single byte. If you want to do single byte read, please follow the workaround in the errata.

Best regards,
Jørgen

[developer1.0]

Hey, thank you for your help. This is really the error, now it works :)

Best Regards,

Florian