MAX7219 and 7 segment LED, what is the correct digit order?

Is digit 0 leftmost or rightmost? I've tried to look up schematic and it seems to be used as left or right. I wanted to make a custom board to use those big 2.1" displays and I don't want to accidentally reverse digit order.

Left right, depends on how you drive it. MAX7219 is just 8 shift registers basically, if you want to wire the digit7 to the right hand digit and treat it as the LSB, you can do that, or wire digit7 to the left hand digit and treat it as the MSB, you can do that.

The larger displays may need more than 5V to drive them if they have multiple LEDs in series to make up a segment. If that's the case and they are individual digits, then a TPIC6B595 high voltage/high current shift register per digit works well for common anode displays, and MIC5891 for common cathode displays.

I have a board that supports up to 12 TPIC6B595 for large displays, with a 328P, plug on an FTDI Basic and treat it like an Uno. The shift registers are wired to be driven with SPI.transfer().

[img alt=2014 12 digit driver board]http://www.crossroadsfencing.com/BobuinoRev17/2014%20board.jpg[/img]

these cheap 0.36 displays

use the right most as digit 0.

 device   0                 1                 2                       7
 addr     0 0 0 0 0 0 0 0   1 1 1 1 1 1 1 1   2 2 2 2 2 2 2 2         7 7 7 7 7 7 7 7
 digit    7 6 5 4 3 2 1 0   7 6 5 4 3 2 1 0   7 6 5 4 3 2 1 0   ...   7 6 5 4 3 2 1 0

 position 0 1 2 3 4 5 6 7   8 9 10            16                      56            63

I would stick to that concept as these displays are really very common.