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2.3.19 Plug and Play Configuration 0

This register allows configurable mapping of the par-

allel port’s interrupt onto the ISA interrupts. Upon re-

set, PNP0 is initialized to 00000xxx.

FIGURE 20. PNP0 Register Bitmap

Bits 2-0 - Parallel Port IRQ Select

These bits are reflected on bits 5-3 of the CNFGB

ECP register. Bit 0 of PNP0 is reflected on bit 3 of

CNFGB.

Upon reset, these bits are undefined.

Microsoft’s ECP Protocol and ISA Interface Stan-

dard defines these bits as shown in Table 20.

TABLE 20. Parallel Port Plug and Play Interrupt

Assignment

Bit 3 - Select Legacy or Plug and Play Mode

Upon reset this bit is initialized to 0. This bit may

be modified only when all modules are disabled. In

both modes, the Chip can decode 11-bit address-

es or 16-bit addresses, according to the strap pin

CFG0. Decoding of 10-bit addresses is not sup-

ported.

0 - Legacy mode. (Default)

The interrupts and the base addresses of the

FDC, SCC1, SCC2 and the parallel port are

configured as in legacy devices, i.e., as in pre-

vious SuperI/O chips. DMA channels are con-

figurable under this mode.

1 - Plug and Play mode.

The interrupts, the DMA channels and the

base addresses of the FDC, SCC1, SCC2

and the parallel port are fully Plug and Play.

Bits 7-4 - Parallel Port Interrupt Mapping

Parallel port interrupt mapping in Plug and Play

mode. Upon reset these bits are initialized to 0000.

When enabled it can be routed onto one of the fol-

lowing ISA interrupts: IRQ7-3, IRQ12-9 and

IRQ15, as shown in Table 21.

TABLE 21. Parallel Port Plug and Play Interrupt

Mapping

Disable means the interrupt of the parallel port is

not routed to any ISA interrupt. Unpredictable re-

sults when invalid values are written. IRQ5, IRQ12

and IRQ15 can not always be configured. For

more details, see Section 6 on page 190.

It is the software‘s responsibility to route all inter-

rupt sources onto the ISA interrupts correctly.

These bits work with bits 2-0, to select the interrupt

destination for the parallel port. However, the ac-

Bit 2Bit 1Bit 0

Interrupt Assignment

Parallel port’s interrupt is

selected by jumpers

IRQ7 is parallel port’s interrupt

IRQ9 is parallel port’s interrupt

IRQ10 is parallel port’s interrupt

IRQ11 is parallel port’s interrupt

IRQ14 is parallel port’s interrupt

IRQ15 is parallel port’s interrupt

IRQ5 is parallel port’s interrupt

Select Legacy or Plug-and Play Mode

Parallel Port IRQ Select

Parallel Port Interrupt Mapping

543

Reset

Required

(PNP0)

Plug and Play Configuration

Index 1Bh

Bit 7Bit 6Bit 5

Bit 4

Interrupt

000

Disable

000

Invalid

001

Invalid

001

IRQ3

010

IRQ4

010

IRQ5

011

IRQ6

011

IRQ7

100

Invalid

100

IRQ9

101

IRQ10

101

IRQ11

110

IRQ12

110

Invalid

111

Invalid

111

IRQ15

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