Lenovo ThinkPad 560E TP 560Z Technical Reference Manual - Page 45
Miscellaneous System Functions and Ports, Nonmaskable Interrupt (NMI), Attention
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Miscellaneous System Functions and Ports This section provides information about nonmaskable interrupts (NMIs), the power-on password, and hardware compatibility. Nonmaskable Interrupt (NMI) The NMI signals the system microprocessor that a parity error or a channel check timeout has occurred. This situation can cause lost data or an overrun error on some I/O devices. The NMI masks all other interrupts. The interrupt return (IRET) instruction restores the interrupt flag to the state it was in before the interrupt occurred. A system reset causes a reset of the NMI. The NMI requests from system board parity and channel check are subject to mask control with the NMI mask bit in the RT/CMOS Address register. See "RT/CMOS Address and NMI Mask Register (X'0070')" on page 2-18. The power-on default of the NMI mask is 1 (NMI disabled). Before the NMI is enabled after a power-on reset, the parity-check states are initialized by POST. Attention The operation following a write to X'0070' should access X'0071'; otherwise, intermittent failures of the RT/CMOS RAM can occur. ThinkPad 560Z System Board 2-27