Little Board P6d Module
2-13
I/O Addresses and Interrupt Assignments
The serial ports appear at the standard port addresses as shown in Table 2-9. Each serial po rt can
be independently disabled using the Setup function, freeing its I/O addresses for use by other
devices installed on the PC/104 and PCI expansion buses. When a serial port is disabled , its I/O
addresses and IRQ are available to other peripherals installed on the PC/104 ex pansion bus. You
can disable any of the serial ports using Setup.
Table 2-9 also shows the IRQs assigned to each serial port.
Note
Serial 3 and Serial 4 ports may use interrupts IRQ10 (PCI) and IRQ12
(PS/2 Mouse), but these IRQs can only be allotted to one device or port
at a time. For example, if you are using IRQ10 for a Serial Port 3 and
also have it assigned to the PCI bus, the serial interrupt will not
occur. You may disable the PCI slot or PS/2 Mouse, to free the IRQ.
Table 2-9. Serial Port I/O Addresses and Interrupts
Port I/O Address Interrupt
Serial 1 3F8h - 3FFh 3, 4
Serial 2 2F8h - 2FFh 3, 4
Serial 3 3E8h - 3EFh 3, 4, 10, 12
Serial 4 2E8h - 2EFh 3, 4, 10, 12
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 desire a serial port, and there is no substitute serial port in the system,
then the ROM-BIOS assigns the COMn designations in sequen ce as it f inds th e seri al ports,
starting from the primary serial port and searching to the last one, Serial 4. Thus, for examp le, if
Serial 1 and Serial 3 are disabled, the ROM-BIOS assigns COM1 to Serial 2 and COM2 to Serial 4.
Serial Port Connectors (J8, J11)
Serial 1 and Serial 2 appear on connector J8; Serial 3 and Serial 4 appear on connector J11. Table
2-10 gives the connector pinout and signal definitions for J8 and J11. Table 2-11 giv es the
RS485/RS422 serial port connections.
The table also indicates the pins to which each signal is wired for compatibility with DB25 and DB9
connectors. The serial port pinout is arranged so that you can use a flat ribbon cable between the
header and a standard DB9 connector. Split a 20-wire ribbon cable into two 10-wire section s, each
one going to a DB9 connector. Normally PC serial ports use male DB connectors. Table 2-12 shows
the manufacturer’s part number for mating connectors.
The RS485/RS422 interface requires that the receiving end of the twisted-pair cable be te rminated
with 100 ohm resistors. You can terminate the RS485 interface with a resistor provided o n the
Little Board P6d module. To terminate the line, install a jumper on W4-W7, as shown in Table 2-13
.