MAX7219 Help

[LgMets10]

Hi ,

I’m working on a MAX7219 LED matrix project using a MAX II CPLD and VHDL.

Right now:

• 1 matrix works correctly
• 2 matrices also work
• but when I connect 3 matrices in cascade, the last matrix shows random garbage or freezes after some time.

Symptoms:

• Sometimes all LEDs turn on
• Sometimes the last matrix flickers randomly
• Sometimes the first two matrices work and the third one freezes
• The animation gradually becomes slower until it stops

What I already checked:

• Shared GND between 5V and 3.3V
• Separate 3.3V regulator for CPLD
• MAX7219 powered at 5V
• SPI clock slowed down a lot
• Added initialization delay (~250ms)
• Clear display commands before sending data
• Tested different FSM implementations

I suspect it may be:

• SPI timing
• cascading timing
• DIN setup/hold timing
• or signal integrity issues

Has anyone experienced something similar with MAX7219 + FPGA/CPLD?

Any advice would help a lot 😅

Thanks!

[Stokpan]

Try my MAX7219x4 component (at Interface.vhd) first. Make the necessary edits for your 3 arrays, make sure MainCLK doesn't exceed the spec, set Matrix 1-3 to test values. Does it work?

[LgMets10]

Thanks for the help

I finally got the 4 MAX7219 matrices working correctly with my CPLD project.
The problem ended up being mostly timing and initialization related.
I slowed down the SPI clock a lot, added startup delays, repeated the initialization sequence, added display-test commands, and also extra latch delays. After that everything started working perfectly.
Your MAX7219x4 example helped me understand the timing much better honestly.
Now I can finally continue with the Arkanoid project