IRQ Assignments, California Computer Advantage, Inc.

California Computer Advantage, Inc.

IRQ Assignments

0 System Timer

1 Keyboard

2 IRQ Cascade to 9

3 COM2 / COM4 (Modem, if present)

4 COM1 / COM3 (Serial mouse, if present)

5 SoundBlaster style sound cards, LPT2 if present

6 Floppy disk controller

7 LPT 1

8 Real Time Clock

9 ACPI controller, SCSI adapter, Video adapter Substitutes for IRQ 2

10 USB Controller, sometimes Ethernet

11 Usually PCMCIA slot devices, sometimes Ethernet

12 PS/2 Mouse

13 Math Co-Processor

14 IDE Primary Controller

15 IDE Secondary Controller

DMA Assignments

0 Available (Sometimes used by Soundcard)

1 Available

2 Floppy Drive

3 ECP LPT Port

4 DMA Cascade Controller

5 Available (Sometimes used by Soundcard)

6 Available (Sometimes used by LT Win modem)

7 Available (Sometimes used by LT Win modem)

I/O Addresses

Within the computer's memory map, certain memory addresses are generally used for certain things. Listed below you will see the common I/O addresses with problems, and what hardware should be assigned to what address. These addresses are in hexadecimal format.

I/O Address	Common Device using Address
130h	Used for SCSI host adapters
140h	Used for SCSI host adapters
170h	Secondary IDE Interface
1F0h	Primary IDE Interface
220h	Typically used for Sound Blaster-type sound cards
240h	An alternate address for sound cards
278h	Assigned to LPT2 or LPT3 and generally used with IRQ 5
280h	Network Interface cards or the Aria Synthesizer
2A0h	An alternate address for NIC cards or the Aria Synthesizer
2E8h	Assigned to COM 4 and used with IRQ 3
2F8h	Assigned to COM 2 and used with IRQ 3
300h	Another Network Interface Card choice
320h	A good place for a Network card, unless there is a SCSI host adapter or MIDI device
330h	A common place for the SCSI host adapters
340h	Another good alternative for the SCSI host adapter
360h	A Network card choice, but beware of the first parallel printer port, this could be a conflict.
378h	The first parallel printer port (LPT 1) in color systems, commonly used with IRQ 7.
3BCh	The first parallel printer port (LPT1) in monochrome systems, beware you may have problem assigning this address to a printer port in Windows 95.
3E8h	Assigned to COM 3 and used with IRQ 4
3F8h	Assigned to COM 1 and used with IRQ 4

After the installation of most hardware, if the system starts to freeze or the additional device does not operate properly, it’s probably caused by a conflict with the IRQ, DMA, or I/O address regions of the new card.

With a thorough understanding of which devices use which system resources, generally a solution can be worked out to allow the new device to work properly.

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California Computer Advantage, Inc.
650 N. Rose Drive #436
Placentia, California
92870