Compaq Contec COM-2(PC)F - Manual (Page 30)

How to Use the Board
COM-2(PC)F
21
Note!
When used in Compatible mode, COM3 and COM4 are not
supported by some programming languages. Check the
specifications of the language you are using. Table 2.1. lists the
COM ports supported by a number of common programming
languages.
Table 2.1. COM Port Support for Various Programming
Languages
Language COM1 COM2 COM3 COM4
Microsoft C O O O O
Quick BASIC O O Ч Ч
GW-BASIC O O Ч Ч
Turbo Pascal O O O O
If writing your own driver software, see "Appendix B : Notes on
Developing Driver Software".