Practice Exercise 18
  1. Your computer has the following peripherals attached to it. 
               keyboard          monitor         speaker
               microphone        mouse           printer
               modem             CD-ROM          hard drive
               floppy drive      PCMCIA card     streaming tape drive
  1. How many ports on the processor chip would it need if only direct (isolated) I/O were to be used?

     

  2. How many contact pads would be needed on the chip if each port were 8 bits wide? Further suppose that each contact pad is 2 millimeters wide. How big would the circumference of the chip need to be in feet? (There are 39.37 inches in a meter and 12 inches in a foot).
  1. List a couple protocols or standards around the house that have to do with communication or electrical devices. Think of both sequences of actions and of physical shapes and sizes.
  1. In the tape reader protocol example, why is it necessary for the CPU to set the DA bit to 1 after it gets the byte from the data port, even if the CPU is always a lot faster than the peripheral? (HINT: Look at the assembler code in Fig. 3 and imagine that the CPU is a lot faster than the peripheral.)
  1. In a certain computer that uses memory-mapped I/O, each device is given 4 addresses because it can have up to 4 registers through which it communicates with the CPU. The addresses from 0...0000100 to 0...1111111 are set aside for memory mapped I/O. How many devices can this computer have attached to it?
  1. Why is location 0 usually never used for memory-mapped I/O?
  1. Refer to Figures 18.7.2 and 18.7.3. Suppose that a new device had to be attached and it was given addresses 00011000 to 00011111 for its registers.
  1. Show the decoder for the device active wire for this device.

     

  2. Show the decoder for the device active wire for memory now.
  1. A certain computer runs at 1 MIPS. The keyboard interrupts it 60 times a second and the keyboard interrupt routine is 50 instructions long.
  1. How many instructions can this computer do in 1/60th of a second?

     

  2. Of the 1 million instructions which this computer will do every second, what percentage is devoted to the overhead of handling the keyboard?