Setting the SCLK of my SPI master

RE: Setting the SCLK of my SPI master

Keven — Tue, 28 May 2019 19:47:38 GMT

Yeah I'm pretty sure I did setup everything fine (CPOL, CPHA are the same on both sides). I'm using the J-link RTT Viewer with the NRF_LOG_HEXDUMP_INFO function to be able to see the bytes I'm receiving. The oscilloscope confirms it. For example, I'm receiving 4F on the first byte instead of 4E.

RE: Setting the SCLK of my SPI master

awneil — Tue, 28 May 2019 19:24:58 GMT

[quote userid="79851" url="~/f/nordic-q-a/47810/setting-the-sclk-of-my-spi-master/189709"]the data I received was wrong[/quote]

In what way(s) "wrong" ?

Have you checked with an oscilloscope that the waveforms are all OK?

Do you have the correct SPI Mode?

RE: Setting the SCLK of my SPI master

Keven — Tue, 28 May 2019 18:13:45 GMT

I tried to plug in the 6.25MHz from my SPI master and the data I received was wrong. Maybe I'm doing something wrong and the data should be right like you said. I'm going to take another look on that.

Thank you for your reply.

Keven

RE: Setting the SCLK of my SPI master

awneil — Tue, 28 May 2019 16:16:49 GMT

[quote userid="79851" url="~/f/nordic-q-a/47810/setting-the-sclk-of-my-spi-master"]SCLK as a value that isn't in the bank of the nRF52840 SPI (125k, 250k, ... 8mbps)[/quote]

Surely, they only apply when the nRF is generating the clock; ie, when the nRF is Master?

If the nRF is the slave, then it receives its clock from the Master; it doesn't have to generate it, so isn't constrained by that list.

The only constraint would be that you don't exceed the maximum clock which the nRF can accept.

RE: Setting the SCLK of my SPI master

Keven — Tue, 28 May 2019 13:53:47 GMT

The formula I'm using is this one :

It's using the clock of my FPGA and divide it by 2 times the clk_div which make things more complicated for me. I should have put that formula in the first place to avoid misunderstanding.

Thank you for your reply,

Keven

RE: Setting the SCLK of my SPI master

Øyvind — Tue, 28 May 2019 07:22:15 GMT

Hello Keven,

Please correct me if I'm wrong, but isn't 100MHz/25 = 4 MHz? Are you running 50MHz? This more correct with regards to the numbers you are mentioning: 50MHz/8 = 6.25 and 50MHz/25=2MHz.

Kind regards,
Øyvind