Interrupts; System Interrupts; Table 2-3 Interrupt Line Assignments - GE V7865 Series Hardware Reference Manual

Table 2-2 V7865 I/O Address Map
I/O Address Range
$3F8 - $3FE
$3FF - $4FF
$500 - CFF
* While these I/O ports are reserved for the listed functions, they are not implemented on the V7865. They are listed
here to make the user aware of the standard PC usage of these ports.

2.5 Interrupts

2.5.1 System Interrupts

In addition to an I/O port address, an I/O device has a separate hardware
interrupt line assignment. Assigned to each interrupt line is a corresponding
interrupt vector in the 256-vector interrupt table at $00000 to $003FF in memory.
The sixteen maskable interrupts and the single Non-Maskable Interrupt (NMI)
are listed in Table 2-3 along with their functions. Table 2-4 on page 33 details the
vectors in the interrupt vector table. The interrupt number in HEX and decimal
are also defined for real and protected mode in Table 2-4 on page 33.
The interrupt hardware implementation on the V7865 is standard for computers
built around the PC architecture, which evolved from the IBM PC/XT. In the IBM
PC/XT computers, only eight interrupt request lines exist, numbered from IRQ0
to IRQ7 at the PIC. The IBM PC/AT computer added eight more IRQx lines,
numbered IRQ8 to IRQ15, by cascading a second slave PIC into the original
master PIC. IRQ2 at the master PIC was committed as the cascade input from the
slave PIC. This architecture is represented in Figure 2-1 on page 37.
To maintain backward compatibility with PC/XT systems, IBM chose to use the
new IRQ9 input on the slave PIC to operate as the old IRQ2 interrupt line on the
PC/XT Expansion Bus. Thus, in AT systems, the IRQ9 interrupt line connects to
the old IRQ2 pin (pin B4) on the AT Expansion Bus (or ISA bus).
32 V7865 Hardware Reference Manual
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Size In Bytes HW Device
7 Super-I/O Chip
256
2048

Table 2-3 Interrupt Line Assignments

IRQ AT Function
NMI Parity Errors
(Must be enabled in BIOS Setup)
0 System Timer
1 Keyboard
2 Duplexed to IRQ9
3 COM2
4 COM1
5 Unused
6 Floppy Controller
7 Unused
8 Real-Time Clock
9 Old IRQ2
10 Not Assigned
11 Not Assigned
12 Mouse
13 Math Coprocessor
14 AT Hard Drive
15 Flash Drive
PC/AT Function
COM1 Serial I/O (16550 Compatible)
Reserved
Reserved
Comments
Used by V7865 PCI bus Interface
Set by BIOS Setup
Set by BIOS Setup
SVGA or Network I/O
Determined by BIOS
Determined by BIOS