This appendix summarizes assignments for IRQ, DMA, and I/O port addresses used by built-in devices on legacy system boards. Contents
The following IRQs used by ISA devices are considered to be fixed assignments.
Fixed ISA Interrupts | |
---|---|
Hardware IRQ | Default assignment |
IRQ 0 | System timer |
IRQ 1 | Keyboard |
IRQ 2 | Second programmable interrupt controller |
(PIC) cascade | |
IRQ 3 | COM 2 |
IRQ 4 | COM 1 |
IRQ 5 | Sometimes LPT 2 - not considered fixed |
IRQ 6 | Standard FDC |
IRQ 7 | LPT 1 |
IRQ 8 | Real-time clock / CMOS |
IRQ 9 | - |
IRQ 10 | Sometimes COM 4 - not considered fixed |
IRQ 11 | Sometimes COM 3 - not considered fixed |
IRQ 12 | PC/2-style mouse |
IRQ 13 | Coprocessor |
IRQ 14 | Primary IDE controller |
IRQ 15 | Secondary IDE controller |
The following table lists DMA channel assignment used by legacy ISA devices and therefore considered fixed.
Legacy ISA DMA considered fixed | |
---|---|
Hardware DMA | System function (default) |
DMA 0 | ISA expansion |
DMA 1 | - |
DMA 2 | FDC |
DMA 3 | ECP parallel port on LPT 1 |
DMA 4 | DMA controller cascading |
DMA 5 | - |
DMA 6 | - |
DMA 7 | - |
The following table lists I/O addresses used by legacy ISA devices and therefore considered fixed.
Legacy ISA System I/O | |
---|---|
I/O Address | Default system function |
0000 - 000F | Slave DMA |
0010 - 0018 | System |
0001F | System |
0020 - 0021 | Master 8259 |
0040 - 0043, 0048 - 004B | PIT #1, PIT #2 |
0050 - 0052 | System |
0060 | Keyboard / mouse controller |
0061 | System control port B |
0064 | Keyboard / mouse status |
0070 - 0071 | NMI Enable / real-time clock |
0081 - 008B | DMA page registers |
0090 - 0091 | System |
0092 | System control port A |
0093 - 009F | System |
00A0 - 00A1 | Slave interrupt controller |
00C0 - 00DE | Master DMA controller |
00F0 - 00F1 | Coprocessor busy clear/reset |
0170 - 0177 | Secondary IDE controller |
01F0 - 01F7 | Primary IDE controller |
0201 | Joystick interface |
0220 - 022F | Sound Blaster |
0278 - 027A | LPT 2 (XT parallel port 3) |
02E8 - 02EF | Alternate COM (4) |
02F8 - 02FF | COM 2 |
0330 - 0331 | MPU-401 |
0376 | IDE Controller |
0378 - 037A | LPT 1 (XT parallel port 2) |
0388 - 038B | FM synthesis |
03B0 - 03BB | MDA, EGA / VGA |
03BC - 03BE | LPT 3 (XT parallel port 1) |
03C0 - 03DF | EGA / VGA |
03E0 - 03E7 | PCIC PCMCIA controllers |
03E8 - 03EF | Alternate COM (3) |
03F0 - 03F7 | FDC |
03F8 - 03FF | COM 1 |
0534 - 0537 | Windows Sound System-compatible |
0CF8 - 0CFB | PCI ports |