Specifications

Hardware Configuration
2–11
Port I/O Address Interrupt
Serial 1 3F8h - 3FFh 4
Serial 2 2F8h - 2FFh 3
Serial 3 3E8h - 3EFh 4 or 12
Serial 4 2E8h - 2EFh 3 or 10
Table 2-6 Serial Port I/O Addresses and Interrupts
2.6.2 Interrupt Assignments
As shown in Table 2-6, interrupt 4 (IRQ4) is assigned to Serial 1 and Interrupt 3 (IRQ3) to Serial 2.
These assignments can be disabled, but they cannot be changed. Serial 3 and Serial 4 can share these
same interrupts, using a “wired-or” configuration, they can use independent IRQs, or they can be
disabled and use no interrupt at all. Jumper options are provided to independently select the wired-or
configuration or independent interrupts for Serial 3 and Serial 4.
Figure 2-4 Serial 3 Interrupt Configuration (W4, W6)
Figure 2-5 Serial 4 Interrupt Configuration (W5, W7)
When a serial port is disabled, leave its jumpers off to make its IRQ available to other peripherals
installed on the PC/104 expansion bus. For information about disabling the serial ports using
SETUP, see Chapter 3.
2.6.3 ROM-BIOS Installation of the Serial Ports
Normally, the ROM BIOS supports Serial 1 as the DOS COM1 device, Serial 2 as the DOS COM2
device, and so on. If you disable a serial port, and there is no substitute serial port in the system, then
the ROM-BIOS assigns the COMn designations as it finds the serial ports, starting from the primary