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SCPA033
PCI1520 Implementation Guide 9
7 Interrupt Configurations
The PCI1520 provides system designers with great flexibility in configuring interrupts. The
PCI1520 allows four interrupt modes which are selected via bits 2:1 of the Device Control
register at PCI offset 92h.
PCI interrupts are available on INTA# and INTB#. These signals are available on MFUNC0 and
MFUNC1 respectively. The Multifunction Routing register at PCI configuration offset 8Ch must
be programmed correspondingly. If MFUNC1 is not available (i.e. EEPROM implementations
which use MFUNC1 as SDA), the INTRTIE bit can be set at bit 29 in the System Control register
at PCI offset 80h. This allows both INTA# and INTB# signaling to both be reported on INTA#.
PCI interrupts can also be signaled through IRQSER.
ISA style IRQ interrupts are available on IRQ15:2. These signals are available on MFUNC6:0.
These interrupts are necessary for some 16-bit PC Cards to function properly. IRQ interrupts
can also be signaled through IRQSER.
IRQSER is available on MFUNC3 and requires a 43k pullup resistor to VCC.
7.1 Parallel PCI Interrupts Only
The parallel PCI interrupts only mode is selected by programming bits 2:1 to a value of 00b.
This allows interrupts to be routed through INTA# and INTB#. This is not a recommended
interrupt configuration because many 16-bit PC Cards require legacy ISA interrupts and will not
function properly.
7.2 Parallel IRQ and Parallel PCI Interrupts
The parallel IRQ and parallel PCI interrupts mode is selected by programming bits 2:1 to a value
of 01b. This allows interrupts to be routed through IRQ15:2, INTA#, and INTB#. This is not a
recommended interrupt configuration because this requires all the multifunction terminals to be
used as interrupts which limits other functions on the PCI1520.
7.3 Serial IRQ and Parallel PCI Interrupts
The serial IRQ and parallel PCI interrupts mode is selected by programming bits 2:1 a value of
10b. This allows interrupts to be routed through IRQSER, INTA#, and INTB#. This is the
recommended interrupt configuration for a PCI add-in card implementation of the PCI1520.
INTA# and INTB# can be routed through the PCI edge connector while IRQSER must be
attached to a Serial IRQ input on the motherboard. If no Serial IRQ input is available, this mode
still allows CardBus cards to function properly. However, many 16-bit cards will not.
7.4 Serial IRQ and Serial PCI Interrupts
The serial IRQ and serial PCI interrupts mode is selected by programming bits 2:1 to a value of
11b. This allows all interrupts to be routed through IRQSER. This is the recommended interrupt
configuration for all designs other than PCI add-in cards. It is the simplest method of routing
interrupts and allows the other multifunction terminals to be used for other purposes.