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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 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 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 (Hex
0070)” on page 2-20. The power-on default of the NMI mask is 1
(NMI disabled).
Attention
The operation following a write to hex 0070 should access hex 0071;
otherwise, intermittent failures of the RT/CMOS RAM can occur.
System Board 2-29