UPGRADING REPAIRING PCs

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Chapter 2—System Components and Configuration
I/O Port Addresses
Your computer’s I/O ports enable communications between devices
and software in your system. They are equivalent to two-way radio
channels. If you want to talk to your serial port, you need to know
which I/O port (radio channel) it is listening on. Similarly, if you
want to receive data from the serial port, you need to listen on the
same channel on which it is transmitting.
One confusing issue is that I/O ports are designated by hexadecimal
addresses similar to memory addresses. They are not memory;
they are ports.
Motherboard and chipset devices are normally set to use I/O port
addresses from 0h to FFh, and all other devices use from 100h to
FFFFh. Table 2.22 shows motherboard and chipset-based I/O port
usage.
Table 2.22 Motherboard and Chipset-Based Device Port Addresses
Address (Hex) Size Description
0000–000F 16 bytes Chipset - 8237 DMA 1
0020–0021 2 bytes Chipset - 8259 interrupt controller 1
002E–002F 2 bytes Super I/O controller configuration registers
0040–0043 4 bytes Chipset - Counter/Timer 1
0048–004B 4 bytes Chipset - Counter/Timer 2
0060 1 byte Keyboard/Mouse controller byte - reset IRQ
0061 1 byte Chipset - NMI, speaker control
0064 1 byte Keyboard/mouse controller, CMD/STAT byte
0070, bit 7 1 bit Chipset - Enable NMI
0070, bits 6:0 7 bits MC146818 - Real-time clock, address
0071 1 byte MC146818 - Real-time clock, data
0078 1 byte Reserved - Board configuration
0079 1 byte Reserved - Board configuration
0080–008F 16 bytes Chipset - DMA page registers
00A0–00A1 2 bytes Chipset - 8259 interrupt controller 2
00B2 1 byte APM control port
00B3 1 byte APM status port
00C0–00DE 31 bytes Chipset - 8237 DMA 2
00F0 1 byte Math coprocessor reset numeric error
To find out exactly which port addresses are being used on your
motherboard, consult the board documentation or look up the settings
in the Windows Device Manager.