florinc:
So why do you think MAX7219 is not covered by that app note?
Maxim uses one datasheet for both MAX7221 and MAX7219. In that datasheet, they also specify (page 6):
Whoah! Too fast! You sped past page five!
Seven Segment Drives and Decimal Point Drive that source current to the display. On the MAX7219, when a segment driver is turned off it is pulled to GND. The MAX7221 segment drivers are high-impedance when turned off.
Bold added.
Semantics. When they say:
The MAX7219 and MAX7221 are identical except for two parameters:
The word "parameters" refers to dynamic behaviours rather than strict hardware functions. Albeit that is a little misleading.
In any case, the reason the MAX7219 is not covered by that app note is that the app note is simply not suitable for the MAX7219. And that is it.
I kind of thought you knew this when in your blog you cited the "Playground" page which points out:
Note that the MAX7221 is definitely preferred over the MAX7219 for this technique. This is because in shutdown, the MAX7221 digit drivers are high impedance, rather than V+ as in the MAX7219.