IBM A40 TYPE 6840, Hardware Maintenance Manual

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ROM and RAM Addresses
Adapter cards with processors can contain RAM and ROM. If the adapter cards
have onboard memory, then the following are true.
v
ROM contains operating instructions for the adapter I/O.
v
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.
Chapter 10. Related Service Information
133