2008 Oct 22
| Buses | Display | DMA | I/O | IRQ |
Plug and Play systems may make their own choices about many DMA assignments. The only place to make DMA resource assignments may be under the specific device's Resource tab within Device Manager in the System Properties of the Control Panel.
| DMA Channel |
Devices |
|---|---|
| 0 | Assigned internal to the system board, you shouldn't be able to use it. |
| 1 | No specific assignment, although its usually used for sound cards, or SCSI host adapters. |
| 2 | Assigned to the diskette drives. |
| 3 | No specific assignment, although its again a common choice for sound cards, network interface cards, or SCSI host adapters. |
| 4 | No specific assignment |
| 5 | No specific assignment, however Sound Blaster-type cards generally use this DMA channel. |
| 6 | No specific assignment |
| 7 | No specific assignment |
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.
| Hex I/O Address |
Devices |
|---|---|
| 130 | Used for SCSI host adapters |
| 140 | Used for SCSI host adapters |
| 170 | Secondary IDE Interface |
| 1F0 | Primary IDE Interface |
| 220 | Typically used for Sound Blaster-type sound cards |
| 240 | An alternate address for sound cards |
| 278 | Assigned to LPT2 or LPT3 and generally used with IRQ 5 |
| 280 | Network Interface cards or the Aria Synthesizer |
| 2A0 | An alternate address for NIC cards or the Aria Synthesizer |
| 2E8 | Assigned to COM 4 and used with IRQ 3 |
| 2F8 | Assigned to COM 2 and used with IRQ 3 |
| 300 | Another Network Interface Card choice |
| 320 | Network card, unless there is a SCSI host adapter or MIDI device |
| 330 | SCSI host adapters |
| 340 | Alternative for the SCSI host adapter |
| 360 | A Network card choice, but beware of the first parallel printer port, this could be a conflict. A Network card choice, but beware of the first parallel printer port, this could be a conflict. |
| 378 | The first parallel printer port (LPT 1) in color systems, commonly used with IRQ 7 |
| 3BC | The first parallel printer port (LPT1) in monochrome systems, beware you may have problem assigning this address to a printer port in Windows 95 |
| 3E8 | Assigned to COM 3 and used with IRQ 4 |
| 3F8 | Assigned to COM 1 and used with IRQ 4 |
Depending on the computer's configuration, add-in devices such as SCSI controllers, sound cards, modems, cd-roms, etc. will want an IRQ line that is already used by another device, and thus we have what is commonly referred to as an IRQ Conflict. The most common IRQ conflicts seem to be between two COM ports, generally a mouse and modem conflict that ends up freezing the mouse whenever the modem is activated.
| IRQ | Device | Comment |
|---|---|---|
| 0 | System Timer | This is the reserved interrupt for the internal system timer. It is used exclusively for internal operations and is never available to peripherals or user devices. If a conflict arises with this IRQ chances are the system board is bad, use a diagnostic program to determine if this is the case. |
| 1 | Keyboard Controller | This IRQ is assigned to the keyboard. Its never available to other add-in cards. Again if this is the problem, its most likely a problem with the system board. |
| 2 | Tied to IRQs 8-15 | This IRQ was assigned to older EGA video cards. Beware, IRQ 9 uses IRQ to communicate with the CPU, therefore this IRQ should rarely be used. Conflicts on this line generally come from trying to use a device on IRQ2 and another on IRQ9 at the same time. If you want to use IRQ2, move any device using IRQ9 to another line like 10 or 11. |
| 3 | COM 2 | This IRQ is assigned to the serial ports: COM 2, and COM 4. Avoid setting other devices to this IRQ since mice, modems, and other devices are set to use this IRQ. |
| 4 | COM 1 | This IRQ is assigned to the serial ports: COM 1, and COM 3. Remember IRQ lines for the most part cannot be shared, so generally you can't have devices on COM 1 and COM 3 that are both active and working |
| 5 | LPT2 or Sound Card | This IRQ is assigned to a secondary printer port LPT2, but in the absence of a second printer port, it is used primarily for sound cards, or as an alternative IRQ for the COM ports |
| 6 | Floppy Diskette Controller | This IRQ is assigned to the diskette controller. Few if any devices leave this IRQ as an option, since most systems have a floppy drive built into them. |
| 7 | LPT 1 | This IRQ is assigned to the first parallel port LPT1, its also made available to other add-in cards, but should not be used for anything except the printer port to avoid conflicts. |
| 8 | Real Time Clock | This IRQ is reserved for the internal real-time clock. This line is never available to other add-in cards. If there is a conflict here, its an indication of a motherboard problem. |
| 9 | Substitutes for IRQ 2 | This IRQ uses IRQ 2 to talk to the CPU, so it has a high priority. Its generally used for network cards. |
| 10 | Not Assigned | This IRQ is left open for network cards, sound cards, SCSI host adapters. |
| 11 | Not Assigned | This IRQ is a common one for SCSI host adapters, but can also be used for a variety of other devices. |
| 12 | PS/2 Mouse Port | This IRQ is used for the PS/2 style mouse port included on many motherboards. If the PS/2 mouse port is enabled in the system's setup program, and you're using a PS/2 connection mouse, don't use this port for anything else, otherwise its an available one. |
| 13 | NPU (Numerical Processing Unit) | This IRQ is reserved for the Numeric Processing Unit (math coprocessor) It is never available for anything else |
| 14 | Primary Hard Disk Controller | This IRQ is assigned to the primary hard drive interface. |
| 15 | Secondary Hard Disk Controller | This IRQ is assigned to the secondary hard drive interface. |
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