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4 BIOS Overview
BIOS Addresses
Although the Setup program can be used to change some of the settings, the
following address map is not completely BIOS dependent, but is determined
partly by the operating system. Note that some of the I/O addresses are
allocated dynamically.
I/O Address Ports Function
0000 - 000F DMA controller 1
0020 - 0021 Master interrupt controller (8259)
002E - 002F NS364 Configuration registers
0040 - 0043 Timer 1
0060, 0064 Keyboard controller (reset, slow A20)
0061 Port B (speaker, NMI status and control)
0070 Bit 7: NMI mask register
0070 - 0071 RTC and CMOS data
0080 Manufacturing port (POST card)
0081 - 0083, 008F DMA low page register
0092 PS/2 reset and Fast A20
00A0 - 00A1 Slave interrupt controller
00C0 - 00DF DMA controller 2
00F0 - 00FF Co-processor error
0170 - 0177 IDE secondary channel
01F0 - 01F7 IDE primary channel
0278 - 027F LPT 2
02E8 - 02EF Serial port 4 (COM4)
02F8 - 02FF Serial port 2 (COM2)
0372 - 0377 IDE secondary channel, secondary floppy disk drive
0378 - 037A LPT1
03B0 - 03DF VGA
03E8 - 03EF COM3
03F0h- 03F5 Floppy disk drive controller
03F6 IDE primary channel
03F7 Floppy disk drive controller
03F8 - 03FF COM1
04D0 - 04D1 Interrupt edge/level control
0678 - 067B LPT2 ECP
0778 - 077B LPT1 ECP
0CF8 - 0CFF PCI configuration space