Re: 3,5" Firmware did not fit the whole screen
One other thing:
The MAX232 is just a logic level converter, between RS232 voltages and TTL/CMOS logic levels
The underlying UART protocol remains the same.
The UART protocol could be described in a paragraph.
USB is a different protocol all together, and ridiculously complex:
There's much more than logic level conversion going on inside the USB-to-UART devices.
USB is fine, so long as somebody else makes it work for me.
UART's are far simpler, easily debugged using something like a $20 scope from JYETech.