Is the ADC card external to the PC? If the MSComm control has control of the DTR / DSR lines, then you can use one those to pulse the serial port. As to the real-time aspect, that depends upon how fast you need the real-time acquisition to take place. A serial port is deterministic in that it can move data at a constant rate, but Windows is not a real-time operating system, so it may take time to receive that data. If you only need a few conversions per second, then you should be fine, depending on how much data there is to move.
