System Resources
This appendix lists the IRQ levels, DMA channels and I/O port addresses.
IRQ level assignments
The direct line to the CPU is called an Interrupt ReQuest (IRQ) level or channel. You'll hear both terms used by technical experts. They mean the same thing. The following table lists the default IRQ level assignments for the computer:
|
IRQ
|
Use
|
Notes
|
|
0
|
Timer
|
|
|
1
|
Keyboard
|
|
|
2
|
PIC #2
|
|
|
3
|
Modem
|
COM port, modem
|
|
4
|
COM
|
COM port, modem
|
|
5
|
Sound system
|
COM port, printer, modem, ECP, MPU*
|
|
6
|
3.5-inch diskette drive
|
|
|
7
|
LPT1
|
COM port, modem, ECP, sound system, or MPU*
|
|
8
|
Real-time clock
|
|
|
9
|
Not Available
|
Reserved for system
|
|
10
|
Available
|
COM port, sound system, MPU, modem
|
|
11
|
External PCI bus
|
modem, sound system, FIR, or MPU*
|
|
12
|
PS/2 mouse
|
|
|
13
|
Math coprocessor
|
|
|
14
|
Hard disk
|
CD-ROM, secondary hard disk,
|
|
15
|
CD-ROM
|
CD-ROM, SelectBay
|
* MPU401 in Desk Station V Plus, if available.
DMA channel assignments
Direct Memory Access (DMA) allows some devices to transfer data to and from memory at high speeds, without using the CPU. Such devices are each assigned a unique DMA channel. The computer has two DMA controllers with four channels on each controller, a total of eight DMA channels.
The following table lists the computer's DMA channel assignments.
|
DMA
|
Use
|
Notes
|
|
0
|
Sound system
|
Choice for sound system
|
|
1
|
Sound system
|
Choice for ECP
|
|
2
|
3.5-inch diskette drive
|
|
|
3
|
ECP
|
Choice for sound system, ECP
|
|
4
|
Cascade from DMA channel 1
|
|
|
5
|
Reserved
|
|
|
6
|
Reserved
|
|
|
7
|
Reserved
|
|
Input/output port address assignments
The CPU accesses input/output devices, such as modems, by reading from them or writing to them. Each command to read or write must specify the address (in memory) for the port. Each device that communicates with the CPU must have a unique I/O port address.
The following table lists the device names and their assigned I/O port addresses for the computer.
|
Port address(h)
|
Device/function
|
Notes
|
|
000-01F
|
82C37: DMA controller 1
|
|
|
020-03F
|
82C59: PIC 1
|
|
|
040-05F
|
82C54: timer
|
|
|
060-06F
|
Keyboard controller
|
060 and 064 for controller 061 for system status port
|
|
070
|
NMI mask register
|
|
|
070-07F
|
Real-time clock
|
|
|
080-09F
|
DMA page register
|
|
|
0A0-0BF
|
82C59: PIC 2
|
|
|
0C0-0DF
|
82C37: DMA controller 2
|
|
|
0E0-0E1
|
PCI bus
|
|
|
0F0-0F7
|
Math coprocessor
|
|
|
100-1EF
|
VGA
|
|
|
170-177
|
CD-ROM (secondary IDE controller)
|
|
|
1F0-1FF
|
Hard disk controller (primary IDE controller)
|
|
|
200
|
Joy stick
|
|
|
202-21F
|
Not used
|
|
|
220-22F
|
Not used
|
SoundBlaster Pro
|
|
240-24F
|
Not used
|
Available for sound system
|
|
260-277
|
Not used
|
|
|
278-27F
|
Parallel PRT 2
|
|
|
280-2E7
|
Not used
|
|
|
2E8-2EF
|
Serial port, or built-in modem (COM4)
|
|
|
2F0-2F7
|
Not used
|
|
|
2F8-2FF
|
Serial port, infrared port, or built-in modem (COM2)
|
|
|
300-33F
|
MPU
|
|
|
340-35F
|
Not used
|
|
|
360-37F
|
Not used
|
|
|
370
|
Controller I/O address
|
|
|
376-377
|
Not used
|
Secondary IDE controller
|
|
378-37F
|
Parallel PRT 1
|
|
|
380-387
|
Not used
|
|
|
388-38B
|
Sound system OPL3 (MIDI)
|
|
|
38C-38F
|
Not used
|
|
|
390-39F
|
Not used
|
|
|
3A0-3AF
|
Bisynchronous 1
|
|
|
3BC-3BE
|
Parallel PRT 3
|
|
|
3C0-3DF
|
CGA, EGA, VGA
|
|
|
3E2-3E3
|
Secondary PCMCIA controller when docked (only in PCIC mode)
|
|
|
3E8-3EF
|
Serial port, infrared port, or built-in modem (COM3)
|
|
|
3F0-3F7
|
3.5-inch diskette drive controller
|
I/O ports 3F6 and 3F7 are used for the hard disk controller
|
|
3F8-3FF
|
Serial port, infrared port, or built-in modem (COM1)
|
|
|
400-47F
|
Not used
|
|
|
480-49F
|
DMA high-page register
|
|
|
530-537
|
Windows sound system
|
|
|
540
|
Not used
|
Available for Windows sound system
|
|
E80-E87
|
Not used
|
Available for Windows sound system
|
|
F44-F47
|
Not used
|
Available for Windows Sound System
|