MicroPython Forum (Archive)

Posted: **Wed Aug 29, 2018 4:24 pm**

I am using a PyBoard 1.1, with the latest 1.9.4 firmware:
MicroPython v1.9.4 on 2018-05-11; PYBv1.1 with STM32F405RG

I try to create an SPI object, but it does not seem to take my initialization.

Here is from REPL:
>>> spi=SPI(1, SPI.MASTER, baudrate=600000, polarity=1, phase=0, bits=16, firstbit=SPI.MSB)
>>> spi
SPI(1, SPI.MASTER, baudrate=328125, prescaler=256, polarity=1, phase=0, bits=16)
>>>

The baudrate is wrong, and there appears to be no firstbit attribute.
Checking on a scope, the baudrate is indeed around 330kHz.
What am I doing wrong?

Posted: **Wed Aug 29, 2018 10:31 pm**

Gordon_Hardman wrote: ↑
Wed Aug 29, 2018 4:24 pm
I am using a PyBoard 1.1, with the latest 1.9.4 firmware:
MicroPython v1.9.4 on 2018-05-11; PYBv1.1 with STM32F405RG

I try to create an SPI object, but it does not seem to take my initialization.

Here is from REPL:
>>> spi=SPI(1, SPI.MASTER, baudrate=600000, polarity=1, phase=0, bits=16, firstbit=SPI.MSB)
>>> spi
SPI(1, SPI.MASTER, baudrate=328125, prescaler=256, polarity=1, phase=0, bits=16)
>>>

The baudrate is wrong, and there appears to be no firstbit attribute.
Checking on a scope, the baudrate is indeed around 330kHz.
What am I doing wrong?

You imported the wrong SPI module.
You have to do

Code: Select all

from pyb import SPI

https://docs.micropython.org/en/latest/ ... l-protocol

Import SPI uses "machine.SPI".

Posted: **Thu Aug 30, 2018 9:49 am**

Note that STM32 SPI cannot provide all baudrates. In fact if a specific baudrate is requested, MPY selects the available baudrate <= requested baudrate. Also note that available baudrates vary with SYSCLK frequency.
All of the above is only true for HW SPI, SW SPI might give finer granularity at lower frequencies. But keep in mind that SW SPI usually consumes more power.
In the given example one could use a baudrate of 2*328125, which is closer to 600000 but obviously greater than 600000.

MicroPython Forum (Archive)

SPI initialization not working

SPI initialization not working

Re: SPI initialization not working

Re: SPI initialization not working