Why 0 devices, but not 1?

Question

I have found a sketch in Wokwi where a MAX7219 LED matrix is used. The sketch subject is to display 0 using <LedControl.h>. I don't understand why it's nessesary to send 0 unlike 1 in fourth parameter in library-object initialization.

LedControl(int dataPin, int clkPin, int csPin, int numDevices=1);

It seems it should be 1 there, but the sketch isn't working in that way.

#include <LedControl.h>
int DIN = 12;
int CS =  11;
int CLK = 10;
LedControl lc=LedControl(DIN,CLK,CS,0);
void setup(){
  lc.shutdown(0,false);

  lc.setIntensity(0,15);

}
void loop(){ 
  byte zero[8]= {0x00,0x1c,0x22,0x22,0x22,0x22,0x22,0x1c};
  printByte(zero);
}
void printByte(byte character []) {
  int i = 0;
  for (i=0;i<8;i++) {
    lc.setRow(0,i,character[i]);
  }
}

score 1 · Answer 1 · answered Feb 05 '24 at 13:30

On this page it says: "The fourth argument to LedControl(dataPin,clockPin,csPin,numDevices) is the number of cascaded MAX72XX devices ... only values between 1..8 are allowed here.".

Examining the LedControl source code at GITHUB, we see in file LedControl.cpp in function LedControl() code which checks for unexpected values for the number of MAX7219 LED Matrix devices used:

LedControl::LedControl(int dataPin, int clkPin, int csPin, int numDevices) {
...
  if(numDevices<=0 || numDevices>8 )
    numDevices=8;

We can see if the number is less than or equal to 0 or is greater than 8 the code defaults to 8 devices. So when passing a 0 the code will detect an unexpected value and create 8 devices by default.

Why 0 devices, but not 1?

1 Answers1