[RESOLVED] MAX7219 SPI Issue



  • Hi,

    Thought I move my previous question in different topic and share the finding here.

    So I bought a MAX7219 and was playing around with the spi-tool. Looking at Arduino code and also 7219 datasheet able to do the following

    // set scan limit
    spi-tool -b 0 -d 1 write 0x0B 0x0f

    // set power ON
    spi-tool -b 0 -d 1 write 0x0C 0x1

    // decode mode
    spi-tool -b 0 -d 1 write 0x09 0xFF

    // test mode
    spi-tool -b 0 -d 1 write 0x0F 0x1

    with the test mode (0x0F) able to turn on all the LED and to turn of use 0x0 for 0x0F register.

    But the funny thing is when I use the write command to write on the first row like so

    spi-tool -b 0 -d 1 write 0x00 0x01

    I see 2 LED turned on in Row 0 which is not right. I'm attaching diagram of which LED turn on when using the following command

    spi-tool -b 0 -d 1 write 0x00 <value>

    Any idea why the LED is not turn on properly ?

    Tested in Arduino and all works fine. I tested with Arduino using the sample code from here https://brainy-bits.com/tutorials/how-to-control-max7219-led-matrix/

    0_1475717122411_Selection_134.png



  • After reading the datasheet looks like I'm using the wrong decode mode. Here are the steps in case anyone is having the same problem

    Following is the wiring

    0_1475720647202_Selection_135.png

    Following is the test bash script

    
    
    #!/bin/sh
    #set power ON
    spi-tool -b 0 -d 1 write 0x0C 0x1
    
    #set scan limit
    spi-tool -b 0 -d 1 write 0x0B 0x0f
    
    #decode mode
    spi-tool -b 0 -d 1 write 0x09 0x01
    
    
    #Set each display in use to blank
    for i in 1 2 3 4 5 6 7 8 9
    do
      spi-tool -b 0 -d 1 write 0x$i 0x0  
    done
    
    for i in 1 2 3 4 5 6 7 8
    do
      spi-tool -b 0 -d 1 write 0x$i 0x11
    done
    
    sleep 1
    
    for j in 0x11 0x22 0x33 0x44 0x55 0x66 0x77 0x88 0x99 0xAA 0xBB 0xCC 0xDD 0xEE 0xFF
     do
      for i in 1 2 3 4 5 6 7 8
      do
        spi-tool -b 0 -d 1 write 0x$i $j
      done
      sleep 1
     done
    

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