Windows NT Hangs Running Display Test from Control Panel

• Microsoft Windows NT operating system version 3.1
• Microsoft Windows NT Advanced Server version 3.1
• Microsoft Windows NT Workstation versions 3.5 and 3.51
• Microsoft Windows NT Server versions 3.5 and 3.51

SYMPTOMS

When you run Display Test in Control Panel, if you move the mouse while Windows NT is testing the display, your computer freezes. This happens only on very fast computers, such as 133 MHz Pentiums.

CAUSE

Your mouse uses level triggered interrupts. Edge triggered interrupts do not have this problem. Windows NT does not support shared IRQs on any non- PCI devices.

Communication across the adapter bus is accomplished thru voltage changes. A signal, such as mouse input, creates a voltage change. That voltage change leads to a system interrupt. Some adapters cards in computers (EISA bus systems, for instance) can be configured to share interrupts. The trigger can be set at the edge (when the voltage change occurs) or slightly later (at the new level voltage).

Setting two adapters at the same interrupt - one at edge, one at level - allows them, in theory, to use the same interrupt without conflict.

PCI architecture is designed to accommodate this technology.

RESOLUTION

If you suspect this may be the problem, contact your motherboard manufacturer to inquire whether your system uses level or edge interrupts.