Bill,

I can't say I've cascaded the MAX7219, but I am using the MAX7221 IC on a project and am relatively familar with the datasheet. Some very silly questions, but important none the less.

You say you paralleled the clock and data lines. I presume by data you mean the LOAD (CS) pin? Is your setup close to that as shown on page 13 of the datasheet?

Are the ISET resistors in place on each IC and appropriately sized for the 7-segments you're using?

Have you tried adding a couple capacitors for filtering?

In a pinch, it sounds like a communication error - I haven't been through your code thoroughly - but when you say you see nothing but 8's in the first display, do the commas also light up? I'm wondering if the IC believes you sent a Display Test Register command.

Again, I apologize if the questions seem silly, but no means am I questioning your abilities - I've just made so many simple mistakes with these things myself it's laughable. Oh, one last thing - are you using a breadboard? I found that when I used long wires for the comms from the PIC to the IC that sometimes the data became junk. When I shortened a wire or made a direct connection between the PIC's pin and the IC's pin, things cleared up.

Do you have a schematic and/or picture of your layout?


-Tony