CSC270  Homework #2

Problem #1

Problem #2

Problem #3

Problem #4

This problem deals with the priority encoder we discussed during our first class.

Assume that four peripherals, a mouse, a printer, a floppy drive, and a hard disk generate interrupt signals that are fed to a processor.

The processor has only three inputs (because of pin limitation), and receives an interrupt signal on its INT input, and two code bits, labeled C0 and C1.

The four interrupt signals from the peripherals are fed to a circuit (priority encoder, or PIC) that outputs the three signals described above to the processor.

                                  PIC
                 |             +--------+
                 |             |        |
            INT  +-------------+        +--------- mouse
                 |             |        |
             C0  +-------------+        +--------- printer
                 |             |        |
             C1  +-------------+        +--------- floppy
                 |             |        |
                 |             |        +--------- hard disk
                 |             |        |
                 |             +--------+

The PIC uses the rules below to generate INT, C0 and C1, responding to the interrupt signals it receives from the four peripherals:
• When one or more interrupt signals are active (high), the INT signal becomes active (high).
• If none of the peripherals are interrupting, then INT is low, and so are C0 and C1.
• If the mouse is the only device interrupting, then INT is high, and C0 and C1 are both low.
• If the printer is interrupting, and neither the floppy nor the hard disk are interrupting, then the PIC generates a high level on INT, and sets C1 to 0, C0 to 1. The PIC ignores the mouse if the printer is interrupting.
• If the floppy is interrupting, and the hard disk is not, then the PIC sets the INT signal high, and sets C1 high and C0 low. The PIC ignores the mouse and printer if the floppy is interrupting.
• Finally, if the hard disk is interrupting, then INT is set hight, and C1 and C0 both high. The PIC ignores the mouse, printer and floppy if the hard disk is interrupting.
• Generate the truth tables for INT, C0 and C1.

• Give the minterm canonical forms of INT, C0, and C1.

• Implement the PIC with AND, OR and/or inverter gates.