I am making a 6x13 LED matrix with 2 MAX7219s. I have seen in some example code people use the SPI pins to communicate with the MAX module, and in other examples the pins used with the MAX are not SPI pins. what is the difference between using SPI and not using SPI for the MAX7219 module?
Please post wiring diagrams.
SPI is faster, but could interfere with other SPI hardware.
Would it interfere with an ISP programmer?
No. It could show strange patterns, if it were selected/enabled while the ISP is used.
I have the CS/LOAD pin hooked up to the MOSI pin, would that cause it to show the aforementioned strange patterns?
MOSI should be the data in pin, your description does not make sense.
Are you using an ISP programmer?
I am using an ISP programmer for the ATmega 328P, but I am also using SPI bus for the MAX7219
Does it show strange patterns while uploading?
Because the 7219 doesn't respect a chip select pin, it will see traffic intended for other things on the SPI lines (its not SPI compatible, basically - for that you need the MAX7221)
Think of the 7219 as more like a 74HC595 shift register (which a latch input).
can I still use the MAX7219 on the SPI bus? I am only using the ISP for burning a boot loader
Do you care if it receives unintended data during burning the bootloader - if not it doesn't matter.
I don't care if it receives any unintended signals as long as it doesn't fry the MAX or ATmega chips