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Controlling an SPI device with the Raspberry Pi
电子禅石 | 2019-11-26 12:00:20    阅读:104   发布文章

The Raspberry Pi has a Broadcom BCM 2835 chip allowing it to interface with SPI devices on its GPIO pins. There are two chip select pins meaning that the Pi can control two devices simultaneously.



19MOSI – master output slave input
21MISO – master input slave output
23SCLK – clock
24CE0 – chip enable 0
26CE1 – chip enable 1

Step 1: Enable SPI on the Raspberry Pi

  1. In your Pi’s terminal, run

    sudo raspi-config
  2. Go to Advanced Options > SPI

  3. Choose “Yes” for both questions then select Finish to exit raspi-config

  4. Either reboot your Pi or run this command to load the kernel module

    sudo modprobe spi-bcm2708

Step 2: Install spidev

Spidev is a python module that allows us to interface with the Pi’s SPI bus.Watch movie online The Transporter Refueled (2015)

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install python-dev python3-dev
cd ~git clone https://github.com/doceme/py-spidev.gitcd py-spidev
make
sudo make install

Step 3: Python script

Finally, we can write and run a python script to control the SPI device.

  1. Create a file called spi-test.py in your favorite editor

    #!/usr/bin/pythonimport spidevimport time
    
    spi = spidev.SpiDev()spi.open(0, 0)spi.max_speed_hz = 7629# Split an integer input into a two byte array to send via SPIdef write_pot(input):
        msb = input >> 8
        lsb = input & 0xFF
        spi.xfer([msb, lsb])# Repeatedly switch a MCP4151 digital pot off then onwhile True:
        write_pot(0x1FF)
        time.sleep(0.5)
        write_pot(0x00)
        time.sleep(0.5)
  2. Make the file executable and run it

    chmod +x spi-test.py
    sudo ./spi-test.py

Notes on spidev

Unless the spi.max_speed_hz field is a value accepted by the driver, the script will fail when you run it. The field can be set to these values on the raspberry pi:



125.0 MHz125000000
62.5 MHz62500000
31.2 MHz31200000
15.6 MHz15600000
7.8 MHz7800000
3.9 MHz3900000
1953 kHz1953000
976 kHz976000
488 kHz488000
244 kHz244000
122 kHz122000
61 kHz61000
30.5 kHz30500
15.2 kHz15200
7629 Hz7629

Two SPI devices can be controlled in python by creating two SpiDev objects, one for each device.

spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 976000
spi2 = spidev.SpiDev()
spi2.open(0, 1)
spi2.max_speed_hz = 976000

https://www.takaitra.com/spi-device-raspberry-pi/

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