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AR-B1551 User’s Guide

2.3 KEYBOARD CONTROLLER

The 8042 processor is programmed to support the keyboard serial interface. The keyboard controller receives

serial data from the keyboard, checks its parity, translates scan codes, and presents it to the system as a byte data

in its output buffer. The controller can interrupt the system when data is placed in its output buffer, or wait for the

system to poll its status register to determine when data is available.

Data can be written to the keyboard by writing data to the output buffer of the keyboard controller.

Each byte of data is sent to the keyboard controller in a series with an odd parity bit automatically inserted. The

keyboard controller is required to acknowledge all data transmissions. Therefore, another byte of data will not be

sent to keyboard controller until acknowledgment is received for the previous byte sent. The “output buffer full”

interruption may be used for both send and receive routines.

2.4 INTERRUPT CONTROLLER

The equivalent of two 8259 Programmable Interrupt Controllers (PIC) are included on the AR-B1551 board. They

accept requests from peripherals, resolve priorities on pending interrupts in service, issue interrupt requests to the

CPU, and provide vectors which are used as acceptance indices by the CPU to determine which interrupt service

routine to execute. These two controllers are cascaded with the second controller representing IRQ8 to IRQ15,

which is rerouted through IRQ2 on the first controller.

The following is the system information of interrupt levels:

IRQ2

Interrupt Level Description

NMI Parity check

CTRL1

IRQ0

IRQ1

System timer interrupt from timer 8254

keyboard output buffer full

Rerouting to IRQ8 to IRQ15

CTRL2

IRQ8:Real time clock

IRQ9:Reserved

IRQ10:LAN adapters(based on PCI INT routing)

IRQ12:Reserved for PS/2 mouse

IRQ13:Math.Co-processor

IRQ14:Hard disk adapter

IRQ3 Serial port(depends on setup assignment)

IRQ4 Serial port(depends on setup assignment)

IRQ5 Reserved

IRQ6 Reserved for floppy disk adapter

IRQ7 Parallel port 1

IRQ15:Hard disk adapter

Interrupt Controller

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