Yes, I have a unique SS/Load pin going to each device. SCK and MOSI go to every part in parallel. That seemed easier to code than running all the data thru all the devices every time to set up the MAX7219s and to update the display registers. You've got 84 IO pins on the Mega, so using 3 more SS pins is not likely to break the bank, is it? Data on MOSI is serially clocked into the MAX7219s by SCK, so that is synchronous. All devices see the data going out, but only the device whose latch line is changing have the data latched into registers.
Yes, type on the serial monitor, as soon as you press Enter it shows up on the display. enter everything as lower case letters. this punctuation is supported
. , : / " ?
If you enter + it stops the display, you can use < or > to manually sroll left & right 1 character.
If you are at the end and enter \ it takes one character off the end. I think it might be of by 1 character tho. I'm still working on it.
Entering = after those restarts the scrolling.
I suppose I could make an Enter Text mode and then a Scroll mode, make it easier to see what is being entered and to back up to make corrections. One of these nights ...