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AR-B1570 User’s Guide
8
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-B1570 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 interrupts 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