8259 Interrupt Sources

The 8259 PIC supports 8 vectored priority interrupts. Each interrupt is described in detail in a separate chapter. These interrupt sources are defined as follows:

INPUT   INT     SOURCE
==========================================================================================
IRQ0    08h     PIT Timer 0 (same as PC)
                See "Int 08h - Timer_0 Hardware Interrupt" for more information.
IRQ1    09h     Forced by software (PC Keyboard) interrupt
                IRQ1 interrupts can be forced by software by setting bit 1 of index 18h.
                This capability is provided so that software can implement a PC
                compatible keyboard scheme.  This interrupt occurs on the rising edge of
                this bit.  See "Int 09h - Keyboard Translate Interrupt" for details.
IRQ2    0Ah     Hornet-specific interrupts including GPIO pads (PC reserved)
                See "Int 0Ah: Hornet-Specific Hardware Interrupt", "Interrupt Source
                Registers" , and "General Purpose I/O" on page 15-545 for more
                detailed descriptions of these interrupt sources.
IRQ3    0Bh     GPIO[24:26] pads if properly configured (PC COM2)
IRQ4    0Ch     UART (PC COM1)
IRQ5    0Dh     GPIO[24:26] pads if properly configured (XT fixed disk)
IRQ6    0Eh     GPIO[24:26] pads if properly configured (PC diskette)
IRQ7    0Fh     GPIO[24:26] pads if properly configured (PC LPT1)
                The 8259 will default to this interrupt vector if the signal requesting
                interrupt has gone away before the interrupt acknowledge cycle.  These
                spurious interrupts should be handled gracefully.