marc jet wrote:

> At that time I didn't think about the "copy .. com1" possibility.

  The problem is that the DOS command "COPY file.hex COM1" provides *no*
handshaking whatsoever, whether you use a 16550A or not.  Either you
provide enough RAM to buffer the whole code, or you run at 300 baud to
allow a full 64ms for the programming algorithm to complete all its
options.  1200 baud (16ms per two characters), even with brilliantly-
written foreground/ background code or a hardware UART, is just a little
close to expect all the operations to be performed.

  The main inconvenience of using 300 baud is not the speed, but the
practicalities of changing the PC baudrate and back.
--
  Cheers,
        Paul B.