include vcomm.inc
VxDCall _VCOMM_TransmitCommChar, <hPort, ch>
or eax, eax
jz error_handler
Sends a high-priority character to a port, ahead of any data in the transmission queue. Uses the C calling convention. This is an asynchronous service.
With most port drivers, this service does not actually send the character before returning, but instead stores it in a special one-character buffer. The service fails if a character specified in a previous call to _VCOMM_TransmitCommChar has not yet been sent.
_VCOMM_GetLastError