CSC270  Lab #5

EXPERIMENT 1: Multiplexer

Implement the following function f of three variables, I0, I1, and Cmd:

        f = I0.Cmd' + I1.Cmd

Connect Cmd to one of the data switches, I0 to the 1Hz clock, and I1 to another data switch. Connect f to a logic indicator.

Label each signal on your kit with a post-it or piece of paper.

What is the truth table for f?

What is the simplified truth table for f?

You have implemented a multiplexer. Explain why it "multiplexes", and how you observe the multiplexing behavior.

EXPERIMENT 2: Strange circuit

Implement the circuit on the left below, and investigate it. Work on this with the other groups and come up with a full description of this circuit:
1. How it behaves,
2. Whether it behaves in predictable ways,
3. What interesting properties it has,
4. How it can be improved,
5. etc.

EXPERIMENT 3: The Oscilloscope

This section will follow a mini lecture on the oscilloscope and its typical features. We will go through each section below in synch, with board presentation and experiments interleaved.

Studying the calibration waveform

• Connect Probe 1 to the calibration test-point, as shown in the picture below:
  

• Press AutoScale
• Observe the waveform. It should look like this picture:

Moving the waveform on the screen.

To move it horizontally, find the Horizontal section on the front panel, and the Delay button. Turn it and observe how the waveform can be translated horizontally.

To move it vertically, find the Vertical section, and turn the Position knob in the Probe 1 column. See how you an move the waveform up and down.

Changing the scale of the waveform.

To change its horizontal scale, locate the Time/Div knob in the the Horizontal section. Play with it and see how you can "zoom" in and out, closer or farther away from the waveform.

To change the vertical scale, locate the Volts/Div button in the Vertical section, and play with it. See how you can squeeze the waveform, or make it grow larger than the screen. Why would we want to make the waveform very large?

Measuring waveforms

Let's start with the timing first.
• Using the previous features, make one period of the waveform fit the whole screen.
• Align the left edge of the waveform to one vertical grid line.
• Measure the number of grid squares separating this edge from the similar edge, one period away.
• Locate the units associated with one horizontal grid square: 100 µs. Multiply this number by the number of squares to get the period.

                 1 grid square = 100 µs
                 1 period = T = _______ squares = _________ µs
  

• Compute the frequency, defined as 1 over the period:

                 frequency = 1/T = 1 / _______ =  ________ Hz
  

  Let's now measure the voltages.

• Move the waveform so that its bottom is aligned with one of the horizontal grid lines.
• Measure the number of squares separating the bottom from the top of the waveform.

                 bottom to top of waveform = _________ squares
  

  Record the unit for vertical squares: ____ V/square, and calculate the peak-to-peak voltage (V p-p):

                 waveform height = _____ squares @ ____ V/square
  
                                 = _____ Volts
  
  

Measurements: The Easy Way!

Could the scope have measured all this for us? You bet!
• Press Auto Scale again to make the scope synchronize itself with the waveform.
• At the top left of the front panel, locate the Measure section.
• Press Time
• Look at the bottom of the screen:

             Source   +---- Time measurements ----+  clear   Next
             1 2 3 4  |   Freq   Period  Duty Cy  |  Meas    Menu
  

• Press the grey button at the bottom of the screen that is right next to Period.
• and... Magic!
• Read the period measured by the scope:

             Period =  _________ µs.  
  

  How close is it to the one you measured?
• Now press the button under the Freq display...
• More magic!
• What is the frequency reported by the scope?

             Freq = ________ KHz
  

• Press the Duty Cycle button. Record the duty cycle:

             Duty cycle = _______%
  

• Press Next Menu
• Press Rise Time
• How fast does the signal go from low to high?

             Rise time <= ________ µs
  

More easy measurements

Let's see what the scope can do with voltage measurements!
• Locate the Measure section at the top left of the front panel again, and press Voltage this time.
• At the bottom of the screen, locate the Clear Meas knob and press it. This will clear any previous measurements.
• Press V P-P to instruct the scope that you want to measure peak-to-peak voltages.

           V P-P = _____________ Volts
  

• Press V avg to measure the average voltage.

           V avg = _____________ Volts
  

• Press Next Menu
• Make sure the Show Meas option is On.
• Press V Max and V Min to measure the min and max voltages.

           V Max = ________ Volts
  
           V Min = ________ Volts
  

• Press V top and V base to measure two different quantities:

           V Top = ________ Volts
   
           V Base= ________ Volts
  

• Explain the difference between V Top and V Max.

Exercise

Find everything there is to know (frequency, period, rise-time, voltage peak-to-peak, average voltage, top voltage, max voltage) about the 1 KHz clock signal on the digital kit.

Capturing Irregular Waveforms

Connect Probe 1 to Test Point 3 on the HP waveform generator. Make sure you connect the ground lead to the Ground test point. The picture below show Probe 1 connected to Test Point 1. Use it as example of how to connect the probe to TP 3.

• Press Auto-scale.
• What a mess!
• Make sure you take a short pause to learn more about what is going on...

  ...

• Welcome back. Play with the holdoff button and increase the delay to about 15 ~ 17 µs until you get a stable waveform, similar to that shown below:
  
• Find the period of the signal using the automatic feature you played with earlier. Is the value indicated by the scope similar to the one you measure on the screen? Why?
• The best way in such a case is to use cursors to measure the exact timing. Press Cursors in the Measure section at the top left of the panel.
• Press the button next to t1 at the bottom of the screen.
• Turn the knob next to the Cursors button and move the vertical cursor to the first transition of the waveform.
• Press t2 and move the second vertical cursor to the same transition, a period away.

  Note: it is very likely that the waveform will "jump" around as you move the cursor. That's okay. Move it until you can pin it down to the same transition the t1 cursor rests on.

• Look up t1, t2, Delta-t and 1/Delta-t at the bottom of the screen.

           t1 = _______    t2 = _______   
  
           Delta-t = _______ 1/Delta-t = ________
  

• What is the frequency of the signal?

           freq = _________  Hz
  

• Use the cursors in the same fashion to measure the high and low voltage levels of the waveform. What is the height of the waveform?

           V p-p = __________ Volts
  

Exercise

Find everything there is to know (frequency, period, voltage peak-to-peak) about the signal present on Test Point #4 of the HP kit.