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Concept
Interrupts in 65xx processors
Résumé
The 65xx family of microprocessors, consisting of the MOS Technology 6502 and its derivatives, the WDC 65C02, WDC 65C802 and WDC 65C816, and CSG 65CE02, all handle interrupts in a similar fashion. There are three hardware interrupt signals common to all 65xx processors and one software interrupt, the instruction. The WDC 65C816 adds a fourth hardware interrupt—, useful for implementing virtual memory architectures—and the software interrupt instruction (also present in the 65C802), intended for use in a system with a coprocessor of some type (e.g., a floating point processor).
The hardware interrupt signals are all active low, and are as follows:
RESETa reset signal, level-triggered
NMIa non-maskable interrupt, edge-triggered
IRQa maskable interrupt, level-triggered
ABORTa special-purpose, non-maskable interrupt (65C816 only, see below), level-triggered
The detection of a signal causes the processor to enter a system initialization period of six clock cycles, after which it sets the interrupt request disable flag in the status register and loads the program counter with the values stored at the processor initialization vector (–) before commencing execution. If operating in native mode, the 65C816/65C802 are switched back to emulation mode and stay there until returned to native mode under software control.
The detection of an or signal, as well as the execution of a instruction, will cause the same overall sequence of events, which are, in order:
The processor completes the current instruction and updates registers or memory as required before responding to the interrupt.
65C816/65C802 when operating in native mode: The program bank register (, the part of the address bus) is pushed onto the hardware stack.
The most significant byte (MSB) of the program counter () is pushed onto the stack.
The least significant byte (LSB) of the program counter is pushed onto the stack.
The status register () is pushed onto the stack.
The interrupt disable flag is set in the status register.
65C816/65C802: is loaded with .
Source officielle
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