The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

10-20

THE

x86 MICROPROCESSORS

The return key code which is produced has a format as shown in Fig. 10.17. This code

is stored in an eight-byte FIFO RAM, where FIFO stands for ‘First-In First-Out’. This

RAM thus stores the key codes in the order in which the keys have been pressed.

A valid keypress also causes an interrupt to be generated on the IRQ line of the chip.

This can be connected to the interrupt line of the processor so as to operate the keyboard

in an interrupt driven mode. Another thing that a valid keypress causes is the increment-

ing of a FIFO count in a status register. This information can be used to verify if the FIFO

contains a ...