Compaq Contec COM-2(PC)F - Manual (Page 36)

Hardware Setup
COM-2(PC)F
27
Table 3.2. lists the I/O address and standard interrupt level settings
for COM1 to COM4 (Compatible mode).
Table 3.2. Example Compatible Mode Settings
Port I/O Address
COM1 3F8~3FF IRQ4
COM2 2F8~2FF IRQ3
COM3 3E8~3EF IRQ4 *1 *1 On the IBM PS/55Z and similar,
COM4 2E8~2EF IRQ3 COM3 uses IRQ3.
Interrupt Level
Note!
If using the PC's RS-232C ports as COM 1 and COM 2 at the same
time as using the CONTEC board as COM3 and COM4, COM3 and
COM4 must be set to interrupt levels other than IRQ3 and IRQ4
because COM1 uses IRQ4 and COM2 uses IRQ3.