Sony AR-B1570 User Manual

AR-B1570 User’s Guide 

8 

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. 
 

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: 

 

Interrupt Level

Description

NMI

Parity check

CTRL1
IRQ0
IRQ1

System timer interrupt from timer 8254

keyboard output buffer full
Rerouting to IRQ8 to IRQ15

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