"Very tricky to get the circuit values correct to keep the triacs firing until the next refesh, there was no tolerance !"

Works it good ?
I think, it must flicker, since there is no synchronization
input for the internal multiplex frequency.


"Putting all the rows on the digit drivers and the segments to the columns ?"

It depends, which the anodes and which the cathodes.
For the software its only 7 registers with 5 bits
or 5 registers with 7 bits (5*7 matrix).
The last version give a little more brightness
and faster transfer (only 5 bytes), thats all.


"...and you would need to switch external transistors to handle the necessary voltage drops"

Only on very big displays.


I used also dot matrix displays controlled with 7 power MOSFETs
and some 74AC299 shift registers. But it consume many CPU time
for multiplexing.



Peter