Problem with ISP on micro:bit

This code works with the Python Editor on their website

# Add your Python code here. E.g.
from microbit import *

buf = bytearray(1)

spi.init()

while True:
    buf[0]=0xa4
    spi.write(buf)
    sleep(20)

these are the output signals (yellow=clock,blue=data)

That's with the default init settings.

But that's with the SPI in the microbit module. I don't know if working with MU is the same or whether you'd need to do something different.

Hi John,

thank you for the experiment. I have done the same and got always the same result I got with MU. This is just an editor specific for micro:bit working on local files but includes all the libraries. Anyway, with the standard editor of microbit.org with your code, downloaded and sent to the board nothing happens. In both cases, using the micro:bit with the controller connected and with a different micro:bit board without any circuit.

As the pin themselves works fine when I use write_digital(), I suppose that there is something or some setting I am not making correctly but I have no idea what can it be done.

Enrico

The only thing I do get SPI working with mu is run an init command during initiallization:

spi.init(baudrate=1000000, bits=8, mode=0, sclk=pin13, mosi=pin15, miso=pin14)

Thank you Doug, I hope this is my mistake and not something stranger. I'll try this afternoon and let you know.

Enrico

Hi Enrico

I have used SPI with the micro:bit a couple of times - with two different 7-seg displays. I can't see from your project what SPI controller IC you are trying to control. If you could post the datasheet for that component it would be helpful.  In addition to the SPI controls, there is usually another pin called chip select or CS on the controller IC to "latch" the data to the display. To send anything to the display you need to take the chip select pin (P0) low, then send the data, then take the chip select pin high again.Here is my micropython code for a MAX7219 controller.

from microbit import *

# setup SPI

spi.init(baudrate=1000000, bits=8, mode=0, sclk=pin13, mosi=pin15, miso=pin14)

# initialisation code

pin0.write_digital(0)

spi.write(b'\x0f\x00')  # enable normal mode and disable test mode

pin0.write_digital(1) # latch data

sleep(300)

With best wishes

Steve

Hello Steve,

thank you very much for your suggestions. I will try immediately. You mention pin0. As far as I know, there is no difference between pin0 or any other digital I/O pin or for some reason that I don't know it is absolutely necessary to use this pin? The reason is that I will use pin0 to generate audio frequency and as far as I know only pin0 can do this easily in the micro:bit.

I am aware of the CS pin (number 12 on the 7219) asI am using the same IC. Now I will test your suggested program and see what happens with pin0. I will update you shortly.

Enrico

Sorry, I chose P0 at random as the CS pin (you can use any unused pin). In your case, just modify my code but connect CS  on the 7219 to (say) P12 on the micro:bit and change my code to:

pin12.write_digital(0) etc etc.

The MAX7219 is quite complicated to get fully working (it has many "modes") but my code snippet will get "test mode" working easily. I have a blog post here that goes into more detail about using this controller with the micro:bit.

Good luck.

Steve

Hello Steve,

Thank you for your support. Now it wkrkw and tomktrow I will setup the software.

Enrico

Hi Enrico

That's great news! "Test mode" looks good   I look forward to following your project to completion.

With best wishes

Steve

Hi Steve,

thank you again. I took a look at the link on your blog and it seems very complete and detailed, I think it is very useful for my project.

Cheers, Enrico