DM>          if TX_free>0 then doswrite(Fport,fchar,1,ret);

Calling DosWrite/Read for each byte is __very__ expensive.  You should try
and combine your ReadChar and ReadBlock (and WriteChar/WriteBlock) so they
use the same buffer (which is emptied by another thread perhaps).

 DM> (*
 DM> Procedure WriteBLOCK(Var buf; Var towrite:longint; Var 
 DM> numb_writ:longint);
 DM>            Note that writeblock has been commented out because the method
 DM>            used is EXTREMELY prone to inaccuracies and 
 DM> loss of characters.
 DM>            Use "Writestring" instead.
 DM> BEGIN
 DM>    doswrite(Fport,buf,towrite,numb_writ);
 DM>    end;
 DM> *)

This is probably because of the write mode that the port is in.   I did not
see any ioctl call in your code to set the write mode (see DCBINFO).

If the write mode is "no wait" when your program starts,  the
code above will probably cause characters to be lost (you don't test to see
how many bytes were actually written).



--- Maximus/2 2.02p1