OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE

Stack

PSW

 

Interrupt Enable Bit

1

Trap Flag

2

CS

SP IP

0 0

3

Processor Status Word

Code Segment Register

Instruction Pointer

CS

IP

Interrupt

Vector

Table

4

A1029-0A

Figure 2-26. Interrupt Sequence

2.3.1.1Non-Maskable Interrupts

The Non-Maskable Interrupt (NMI) is the highest priority interrupt. It is usually reserved for a catastrophic event such as impending power failure. An NMI cannot be prevented (or masked) by software. When the NMI input is asserted, the interrupt processing sequence begins after ex- ecution of the current instruction completes (see “Interrupt Latency” on page 2-45). The CPU au- tomatically generates a type 2 interrupt vector.

The NMI input is asynchronous. Setup and hold times are given only to guarantee recognition on a specific clock edge. To be recognized, NMI must be asserted for at least one CLKOUT period and meet the correct setup and hold times. NMI is edge-triggered and level-latched. Multiple NMI requests cause multiple NMI service routines to be executed. NMI can be nested in this man- ner an infinite number of times.

2-42

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Intel 80C186XL, 80C188XL user manual Stack, Psw, Interrupt Enable Bit, Trap Flag, Sp Ip