Spring 2000
ENSC 151
DIGITAL AND COMPUTER DESIGN LABORATORY

Assignment #2(a): Handling Interrupts

Posted: February 1, 2000
Due: Monday, February 14, 2000, by 16:00 in the ENSC departmental office

The given interrupt example program IRQ.ASM sets up IRQ interrupts and then prints ``Press a button!'' on line 1 of the LCD device. It then waits for an IRQ interrupt (blue push-button). When an IRQ interrupt event occurs, the program prints ``Excitting, Eh?'' on line 2 of the LCD device. In-between interrupts it does nothing but waste time in a "busy loop".

Modify the program IRQ.ASM so that it prints one of your user defined characters (from Assignment #1) each time the push-button is pressed, up to a maximum of 8 chars. After that it should not print anything when the push-button is pressed.

Use your ``best'' coding habits. You can modify any part of the IRQ.ASM program. Note: you most likely have to set the top bit of control register INTCR (located at $001e). See page 53 in the 6812 technical summary. Otherwise, your active low push-button may trigger several interrupts before you can take your finger off of it.

Last modified: Monday January 31 21:28:14 PST 2000.