Intel 80C188XL Nmi Cpu, Maskable Interrupt Request Interrupt Acknowledge, Interrupt Control Unit

Models: 80C186XL 80C188XL

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2.3INTERRUPTS AND EXCEPTION HANDLING

OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE

2.3INTERRUPTS AND EXCEPTION HANDLING

Interrupts and exceptions alter program execution in response to an external event or an error condition. An interrupt handles asynchronous external events, for example an NMI. Exceptions result directly from the execution of an instruction, usually an instruction fault. The user can cause a software interrupt by executing an “INT n” instruction. The CPU processes software in- terrupts in the same way that it handles exceptions.

The 80C186 Modular Core responds to interrupts and exceptions in the same way for all devices within the 80C186 Modular Core family. However, devices within the family may have different Interrupt Control Units. The Interrupt Control Unit handles all external interrupt sources and pre- sents them to the 80C186 Modular Core via one maskable interrupt request (see Figure 2-24). This discussion covers only those areas of interrupts and exceptions that are common to the 80C186 Modular Core family. The Interrupt Control Unit is proliferation-dependent; see Chapter 8, “Interrupt Control Unit,” for additional information.

NMI

CPU

Maskable

Interrupt

Request

Interrupt

Acknowledge

Interrupt

Control

Unit

External

Interrupt

Sources

A1028-0A

Figure 2-24. Interrupt Control Unit

2.3.1Interrupt/Exception Processing

The 80C186 Modular Core can service up to 256 different interrupts and exceptions. A 256-entry Interrupt Vector Table (Figure 2-25) contains the pointers to interrupt service routines. Each en- try consists of four bytes, which contain the Code Segment (CS) and Instruction Pointer (IP) of the first instruction in the interrupt service routine. Each interrupt or exception is given a type number, 0 through 255, corresponding to its position in the Interrupt Vector Table. Note that in- terrupt types 0–31 are reserved for Intel and should not be used by an application program.

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Intel 80C188XL, 80C186XL user manual Nmi Cpu, Maskable Interrupt Request Interrupt Acknowledge, Interrupt Control Unit