Start Copy the PC to the MAR Copy the contents of memory at address MAR to IR; Increment PC by 1 Decode the instruction and place bits IR[11-0] in MAR Yes No Instruction requires operand? Copy the contents of memory at address MAR to MBR Execute the instruction FIGURE 4.11 The Fetch-Decode-Execute Cycle Has an Yes No interrupt been issued? Process the interrupt Perform fetch- decode-execute cycle FIGURE 4.12 Fetch-Decode-Execute Cycle with Interrupt Checking

What is the purpose of interrupts? What are the differences between a trap and an interrupt? Can traps be generated intentionally by a user program? If so, for what purpose?

Number 3 please

An ADC produces an interrupt request and the interrupt service routine runs and acquires a burst of data of 10 data values into a global array. What is a good way for the ISR to tell the main program there is new data in the array? Set a global flag variable. Do nothing. The main program has to check if the data array has changed. Pass the array as a return value from the ISR. Clear the interrupt flag in the ADC.