CE121--Microprocessor System Design
Assignment 1
Out: January 8, 1996
Due: January 15, 1996

Reading: Class notes, lab assignment, CE100 notes, Slater 7.2, 2.8, 3.1, 3.2.

1. (20 points) An LED (text section 7.2) has a voltage drop of 1.6V at 20mA (Since diodes, light-emitting and otherwise, are non-linear, we must specify both the current and the voltage, as shown in Figure 7.7; a single number cannot characterize a diode). What should be if ? Draw a labeled diagram (including pinouts and resistor values) of 8 LEDs connected to a 74LS373. Check the databook on how much current the 73LS373 can source or sink.
2. (50 points) Consider the below circuit composed of 2 74LS04 inverters, 3 resistors and 2 capacitors.

   

   1. In terms of , , , , and , write the equation of the circuit's time constant.
   2. Suppose that all resistors are 1k and all capacitors are 0.1 F. What is the time constant?
   3. Assume inverter output is either 0V or 5V, and the inverter threshold voltage (where it switches from low to high) is 1.6V. If the input signal goes from high to low instantaneously, how much latter will the output signal go from high to low? How about if the input signal goes from low to high? Use the equation for charging and discharging an RC circuit to find when it passes 1.6V.
   4. If the input signal is square wave with period of 0.4ms, describe and diagram the output.
   5. Suppose instead that the inverter has typical output voltages of , and . How does this change the previous problem? (One way to deal with the non-zero starting point on charging the RC circuit is to subtract off the time it takes to rise from 0V to 0.25V. When dealing with exponentials, always check the boundary conditions of t=0 and to catch simple errors.)
3. (20 points) The following is an incorrect timing diagram for a microprocessor's read and write cycles. Assume that the read and the write signals are correct. Consider each of the other signals with respect to the read and the write and state anything that is incorrect. Label read versus address, data out, and data in as parts (a)-(c), and write versus address, data out, and data in as parts (d)-(f).

   

4. (10 points) Grader's discretion. From a base of 5 points.

             Lack of staples      -2
             Rough paper edges    -2
             No name              -5
             Hard to read writing -2
             Answers only-no work -20 (or more)
   
             Typeset              +3
             Graph Paper          +1
             Straightedge         +1
             Neat writing         +1
             Clearly marked answers +1
             Clear writing explaining steps or design +2