COCO ACTIVITIES FOR SESSION 8

Names of Team Members / Student ID Numbers / Section

Today:

1. TTL Gates and Data Sheets (Sec.3.5)

Activity 8.1 – Reading data sheets, and LogicWorks™ simulation

2. Working with Hardware

Activity 8.2 – Build and test a combinational logic circuit with real hardware

Hand in Today for Grading:

Activities 8.1, 8.2 (one per team, signed off by your TA).

Read for Next Class:

Section 4.1,4.2 until 4.2.3

8.1 / 8.2 / Sum

______

Grader’s Signature

Activity 8.1: TTL Gates and Data Sheets (Sec.3.5)

Using the attached pages from the TTL data book, or preferably, from the data book itself[1], answer the following questions.

a. (6 points) Use the index, or the section titled “selection information” to locate the part numbers for the following devices. For each case, keep in mind that we need the “LS” type of devices. LS stands for “low-power schottky”, and this is the type that is available in the laboratory.

The first one has been done for you.

Description of the device / Part Number
A chip with four 2-input NAND gates with standard two-state outputs, and standard voltage levels. / 74 LS 00.
We found this on page 1-3 of the Selection Guide. We looked up a table for “NAND gates” and picked out “Quad 2-input NAND gates”. Then, we looked up “2S” in the second column and then checked the fourth column to make sure that this part was available in low-power schottky (“LS”). Then, we read off the number “00” from the third column. The part number is always of the form “74LSxx”. The detailed description of this part is on page 5-2 of the TTL data book.
A chip with 2-input Exclusive OR gates with standard two-state outputs, and standard voltage levels.
A chip with 4-input AND gates with standard two-state outputs, and standard voltage levels.
A chip with 4-input OR gates with standard two-state outputs, and standard voltage levels.
Hint: If you cannot find a part that directly fits your needs, look to other manufacturers first, and then consider synthesizing the part yourself out of other available parts.

b. (20 points) Study the detailed description for the 74LS00 chip with standard two-state outputs, and standard voltage levels, and answer the following questions.

Question /
Answer
How many pins does this chip have? We usually use the plastic or ceramic packaging in the laboratory.
How do we recognize pin #1?
To which pin(s) do we apply power?
Which pin is set to ground (0 volts)?
What is the typical power supply voltage?
What is the worst-case gate delay for this device?
What range of input voltages are considered “Logic 0”?
What range of input voltages are considered “Logic 1”?
List all the input pins on this chip by pin number
List all the output pins on this chip by pin number


c. (10 points) Consider the following combinational circuit:

Build and test this circuit using LogicWorks using the “7400 devs” library instead of the “primgate” library that you have used before. Demonstrate that your circuit has the correct truth table by writing down the Boolean expression for the above circuit, and tabulating the expected and observed outputs in the table below. This would be a simulation of a circuit built using the “74xx series” TTL logic gates.

Boolean Expression for Z = ______

X / Y / Z from Boolean Expression / Z from Logicworks simulation
0 / 0
0 / 1
1 / 0
1 / 1

Attach a printout of your schematic, with the names of the team members clearly indicated.

Activity 8.2: Working with Hardware

In this activity, we will build and test the same circuit as in Activity 8.1, but this time with real hardware. Follow the steps listed on the attached pages. Show your working circuit to the grader and have the following table filled in.

Hardware Activity Signoff Sheet

Hardware works as specified (10 points)
Clean and organized wiring (5 points)
Good circuit layout (5 points)
Supply bypass capacitors were wired correctly (5 points)
Cleanup was done properly(5 points)
Total

______

Grader’s Signature

Computer Components and Operations, Fall 1998 Page 6

COCO LABORATORY PRACTICES

Step 1: Obtaining the equipment

One team member should go to the left back door of the studio and check out a “prototyping board”. You may need to deposit your Rensselaer ID card for this with the TA. You must write down the names of the team-members on this board. You will use this protoboard for the duration of this course, and it should be returned in the same condition you received it in.

Another team member should go to the right back door of the studio and check out a toolbox. Again, you may need to deposit your Rensselaer ID card for this with the TA. The toolboxes will be shared between students in other sections as well as students in other courses, and should be handled very carefully.

The chips are stored in the cabinet on the left end of the studio in labeled boxes. You must return the chips to the proper boxes after use. A list of all available devices is attched at the end of this handout, and is also available from the course web page.

Step 2: Getting to know the equipment

A. The toolbox

The toolbox consists of the following items:

Multi-meter / Use this to measure voltages, resistances, currents, etc.
Logic probe / Use this to probe the logic levels (0 volts and 5 volts). Connect the red wire to +5volts, and the black wire to ground (0 volts). Touch the tip of the probe to a part of your circuit to determine its logic level. The small lights on the probe indicate the logic levels.
Wire stripper / Use this to strip the plastic insulation off wires. Make sure that the stripped plastic is properly disposed of in the trash can.
Wire cutter / Use this to cut wires. Make sure that the small wire pieces are properly disposed of in the trash can.
Long nose pliers / Use this for bending wires.
Chip puller / Use this carefully to pull chips off the protoboard.
Screw driver / Use this to adjust device such as trimmed potentiometers.
Power leads / Use these to connect the power supply to the universal protoboards. Use the following color convention: Red: +5 volts; Green/Black: Ground (0 volts);
Purple: -12 volts; Yellow: +12 volts.

B. The prototyping board

You will do all your wiring on Universal Protoboards (prototyping boards). These boards (see Figure 1) were custom fabricated at RPI for this course. The parts labeled and will be needed for the second half of this course and we’ll not worry about them now.

You will build all your circuits in the areas labeled and . This area consists of an array of holes separated 0.1 inch from each other. The pins on integrated circuits (ICs), commonly referred to as “chips” are also separated 0.1 inch. The holes on the protoboard are connected internally in rows and columns as explained below.

The areas labeled in Figure 1 have two columns of holes each. These holes are connected together lengthwise, as indicated in Figure 2. These buses are usually used for power and ground connections. Do not place components such as integrated circuits (ICs) on this bus.

Figure 1: The universal protoboard that you will use in the laboratory.

The areas labeled in Figure 1 have holes that are connected in the other direction. This part of the protoboard is where you will place ICs and discrete components such as resistors, capacitors, etc. Refer to Figures 2 and 3 for proper placement and connection of ICs. In these figures, there is a +5V "bus" and a GND "bus". Any wire connected to this bus will be connected to either +5V or GND (provided these power signals have been connected from the power supply). It is a good practice to always use red colored wires for +5V lines and black wires for GND lines. The black object in these diagrams represents an IC (Integrated Circuit) which you will use in this course. All ICs have a notch or dot at one end that helps us figure out their orientation. The pins are usually numbered counter-clockwise starting from the pin below the notch (when viewed from above). For instance, Figure 3 shows pin number 11 of this IC connected to GND, and pin number 22 connected to +5V.

Figure 2: Showing how the protoboards are wired internally (shown by the thick arrows), and also the procedure for placing chips.

Figure 3: Showing the connection of ICs. In particular, this diagram shows pin number 11 of this IC connected to GND, and pin number 22 connected to +5V.

Some guidelines for wiring circuits

·  Plan your layout in advance: Look at the way the pins are arranged on each chip and try to place your chips on the protoboard so that they can be connected easily.

·  Modular layout: When you have to build a large circuit, it makes sense to build it in small pieces (“modules”) that can be tested independently, and subsequently connected together. Later, when you are trying to debug your circuit, it makes sense to disconnect the major modules, and test them independently. Try to plan your layout with such modularity in mind.

·  Test each part beforehand: It is often possible for you to encounter chips that are defective. It is a good idea to test each chip before it goes into a complicated circuit. It is a lot harder to locate a defective chip later!

·  Color coding of wires: Be very neat, and follow a systematic color scheme for your wires (see Figure 4 below). For instance, the color red is typically used for +5volts and black is usually used for Ground (0 volts). Use other colors in a systematic manner. This will help you debug your circuits more easily.

·  Avoid “loops”: Try to connect any pair of points in your circuit with a wire that runs close to the protoboard, and is as short as possible. Whenever we have wires that stick out to form “loops” on the board, we run the risk of this loop acting as an antenna, and introducing unwanted electrical disturbances into our circuits.

Figure 4: An example of good wiring.

·  Use supply bypass capacitors: Ideally, the power supply is a rock-steady voltage waveform at +5V and 0V. In practice, however, the supply waveform is "noisy", i.e., it has a small rapidly-fluctuating component. This fluctuating component is usually because of surge currents drawn by each of the little transistors in our digital system, and because of the inability, due to high inductance, of the power supply to meet these surge current requirements. Also, every now and then, one may find large transient fluctuations. These effects can sometimes become large enough to cause unwanted changes in our digital circuit. "Supply Bypass Capacitors" help us in this regard. A capacitor has a high impedance to dc and a low impedance to voltage fluctuations. Putting a large (eg. 0.1mF) capacitor between the +5V and ground pins of your chips effectively short circuits the fluctuations without affecting the steady dc voltage. We can think of bypass capacitors as storing charge that can be used to quickly supply surge current needs.

When wiring supply bypass capacitors, we need to be careful!! Here’s why. When you pick a large (0.1mF – 10mF ) capacitors, you are most probably using an “electrolytic capacitor”. Electrolytic capacitors cannot handle positive and negative voltages. They are usually marked quite clearly with plus "+" and/or minus "-" symbols to indicate their preferred polarity. You can damage them by wiring them with reverse polarity. Usually, the damage is accompanied with overheating and sometimes, a small explosion!!

C. The switches on the universal protoboard

The upper left part of the universal protoboard consists of an array of switches and two push-buttons. They are described in detail below. It is suggested that you use the logic probe tool in your toolbox to get to know the operation of these devices.

Switches 1,2,3 and 4: These are toggle switches that behave as follows.

When the switch is in the “A” position, the “COM” line is connected to “A”. When the switch is in the “B” position, the “COM” line is connected to “B”. These switches can be made to stay in either position for as long as we wish.

Switches 5,6, and 7 (“momentary toggle switches”): These switches are similar to the first four switches except for the fact that they are spring loaded. They ordinarily stay in the “A” position, as shown below.

Normal Position

When operated, they do two things, as illustrated below:

·  disconnect “COM” from “A” for as long as the switch is pressed;

·  connect “COM” to “B” for as long as the switch is pressed.

When Pressed

Here are two ways to wire them up for use:

Switches 8, 9: These are push-button switches, and have only two connections “A” and “B”, as indicated below.

/ / Button not pressed means no connection between A and B.
/ Button pressed means A and B are connected as long as the button is held pressed.

How you wire up a push-button switch makes a difference. You can wire up a push-button as either a "high asserting" or "low asserting" switch as shown below.