!PC has troubles with serial line, and sometime it freezes the kb

I’d like to write a few C/Pascal sources in order to verify the serial line is fully working under !PC/Pro. I do not trust it is, especially with breaks, also I’d like to check how good is the PIC under PC.

From your description, I suspect the timing will be your program. A handshake phases lasting 50msec will be problematic on anything that isn’t running straight DOS (no NTVDM or DOSbox) talking directly to hardware.

About PC-DOS, i’d like to know why/where it’s better than MSDOS, because I have to purchase it (more money).

Prior to v7.1 (IIRC), it was an IBM rebadged version of MS-DOS. Afterwards, it added support for a different style of on the fly compression; and IIRC the later versions also directly support FAT32.