"To minimize power-supply ripple due to the peak digit driver currents, connect a 10?F electrolytic and a 0.1?F
ceramic capacitor between V+ and GND as close to the device as possible. The MAX7219/MAX7221 should
be placed in close proximity to the LED display, and connections should be kept as short as possible to
minimize the effects of wiring inductance and electromagnetic interference. Also, both GND pins must be
connected to ground."
I'm also curious about driving dual color matrix. Typically a matrix would have a shared cathode and 2 sets of anodes for the 2 colors, so 24 pins total on the matrix.
You can't really share the cathodes between MAX7219s by alternately putting each chip into shutdown - they don't stop driving their outputs.
I could see doing that with a MAX7221:
"When the MAX7219 is in shutdown mode, the scan oscillator is halted, all segment current sources are pulled to
ground, and all digit drivers are pulled to V+, thereby blanking the display. The MAX7221 is identical, except
the drivers are high-impedance. Data in the digit and control registers remains unaltered. Shutdown can be
used to save power or as an alarm to flash the display by successively entering and leaving shutdown mode. For
minimum supply current in shutdown mode, logic inputs should be at ground or V+ (CMOS-logic levels)."
I suppose if the cathodes were only weakly driven high, the 2nd device could pull it low.
The software would have to coordinate which device was shut down to prevent drive conflicts.
In Shutdown:
Digit Drive Source Current (MAX7219 only) IDIGIT. Digit off, VDIGIT = (V+ - 0.3V): -2 mA minimum
Segment Drive Sink Current (MAX7219 only) ISEG. Segment off, VSEG = 0.3V: 5 mA
When Active:
Digit Drive Sink Current IDIGIT. V+ = 5V, VOUT = 0.65V: 320 mA min.
So I suppose if 1 part is sourcing -2mA to make the cathode High, and the other is pulling 320mA to make it Low, it's going Low!
That would achieve one color or the other - would alternating quickly give the perception of combined color?