IBM 689912U Hardware Maintenance Manual - Page 465

Queues interrupt request. IRQ conflicts occur when there are multiple assignments to the same interrupt level. If there is an IRQ conflict, the system will hang. Use the systems diagnostics to check for multiple assignments to the same interrupt level before replacing any hardware component. DMA: Accesses the memory by bypassing the processor, which allows the processor more time for applications and programs. Accesses memory directly from the serial and parallel ports on some systems. Accesses memory directly from some adapters using a DMA channel, which allows the adapter to operate faster. Provides from 4 to 15 DMA channels, the number varies depending on the system. If multiple assignments of the same DMA channel occur, the system will hang. Use the system diagnostics to check for multiple assignments to the same DMA channel before replacing any hardware components. I/O Address: A unique I/O address is assigned to each system component. If multiple assignments of the same I/O address occur, the system will hang. Use the DOS MEM command to check for multiple assignments to the same I/O address before replacing any hardware component. ROM and RAM Addresses: Adapter cards with processors can contain RAM and ROM. If the adapter cards have onboard memory, the: ROM contains operating instructions for the adapter I/O. RAM is used for buffering. Two adapters using the same memory area will cause a failure. This failure might appear as a hardware failure. The IRQ levels, DMA channels, I/O address, and ROM and RAM addresses all become potential conflicts and system problems. When conflicts arise, they might show up as system hangs, lost or missing devices, incorrect or bad data, or failing diagnostics. Always eliminate conflicts in these areas before replacing any hardware components. Reference Information 455