ECE Digital Logic Design. Laboratory Manual

Transcription

1 ECE 1315 Digital Logic Design Laboratory Manual Guide to Assembling your Circuits Dr. Fernando Ríos-Gutiérrez Dr. Rocio Alba-Flores Dr. Chris Carroll Department of Electrical and Computer Engineering University of Minnesota Duluth 6/2002 1

2 V. - Guide to Assembling your Circuits. In this section we describe the use of the breadboard and give basic hints about the wiring process needed to power up and interconnect your circuits. Assembling circuits on your breadboard is a fast and easy process once you get used to it. To assemble your circuit first select the chips that you need, insert them in the breadboard, wire up the power and ground connections as described in the next section and next wire the logic elements according to the circuit connections that you obtained from the design process. Before you insert a chip into the breadboard, make sure it is properly oriented (see Fig. 9 & 10), and that when you press it down the pins of the chip actually enter the holes and do not bend underneath the chip package. When wiring, be careful to hit the right hole needed in the connection, because this is one of the most common mistakes found to cause an error in your projects Breadboard Description. In order to assemble the lab experiments, every student should use his/her own breadboard (similar to the one shown in Figure 6). The breadboard has 8 sets of rows (1) and (2), consisting of 25 holes that are horizontally interconnected, and groups of columns (3) and (4), consisting of 5 holes that are vertically interconnected. The rows and columns are used to hold chips and wires, and interconnect them as shown in Figures 7 and Fig Breadboard Also, in Figures 7 and 8 we show two typical ways to distribute power (1), and ground (2) signals that are recommended in order to avoid noise in your circuit, and assure good performance from the chips. The banana plugs (3), if available, can be used to connect your breadboard to an external power supply (usually the Heathkit board). 2

3 3 1 2 Fig Power and Ground Connection (method A) Fig Power and Ground Connection (method B) TTL Packages Description. The chips or packages that will be used to build the experiments belong to the TTL logic family, and they are referred as the 74LSXX family, where the XX is a number that indicates the specific kind of gate or function. The main characteristics for some typical logic gates packages are shown in Figures 9 and 10 next. 3

4 Fig Inverter (NOT) gate pin distribution Fig AND gate pin distribution Most commonly used TTL devices have their power and ground connections on pins 14 and 7 respectively, however verify this information before using some special function or uncommon packages. Also, all packages have a notch or mark that indicates the proper orientation of the device. From this mark each pin is numbered in a counter clockwise direction. The specific function that each chip performs is typically described using function tables, logic tables or logic diagrams as the ones shown in Figure 11. 4

5 Fig Typical Manual Descriptions for a TTL Gate. 5

6 Diagrams and Labeling. Using the pin distribution for the TTL packages given by the manufacturer, and once that you design the circuit that performs the desired logic function, the next step is to wire up the circuit that implements this function. Because every chip has a different number of gates, a good implementation step is to make a diagram for the circuit and label all inputs, outputs and gates in the way shown in Figure 12. By doing this the wiring and testing process will be done very easily in the lab. Pin Number Package Label Gate Name Fig Package, gate and pin labeling There are many methods than can be used to label a circuit. In this manual we show only one that is easy to understand and implement. In this method, every input and output pin shown in the diagram shows the respective pin number that corresponds to the gate in its package. The gates are labeled using a letter and a number. The letter labels a specific gate inside the package, and the number labels the package corresponding to its order. This is shown in Figure 13. For Figure 13, the gate labeled A1 means gate A in chip 1, B1 means gate B in chip one, and A2 means gate A in chip 2 and so on and so forth. Using this information it is very easy to wire the circuit on the breadboard since you only need to place the chips on the breadboard following the order that the chip was given on the diagram. Next, you only need to connect a wire between the pins that are given for every chip. For example, a wire has to be connected between pin 6 of the third chip (B3) and pin 9 of the fourth chip (C4). Another wire has to be connected between pin 8 of the first chip (C1) and pin 5 of chip number 5 (C5), and so on and so forth. Labeling the circuit in this way also makes it easier to find errors on the wiring during the testing process. Another important characteristic that can be noticed from this diagram is that the flow of interconnections and signals follows a left to right direction. This means that typically 6

7 in an electric connection diagram, the inputs will be shown on the left and outputs will be shown on the right. The reason for this is that in this way it is easy to follow the flow of signals in the circuit, and the function implementation at every step that each gate performs. On other hand, it makes the circuit interconnections to appear clearer. Fig Circuit Labels and Connections VI. - IC packages and Lab Inventory. In the Table 1, we show the TTL inventory for the chips available in the lab that can be used in the implementation of your circuits. For some lab experiments you will be informed about which chips you can exclusively use for that project in particular, otherwise you can use any package that is given in the list. Also, a quick reference guide for some of the most common devices is shown in Figure 14. 7

8 NAME FUNCTION NAME FUNCTION 74LS139 DUAL 2-->4 DECODER 74LS00 2 INPUT NAND 74LS >3 DECODER 74LS02 2 INPUT NOR 74LS >1 MULTIPLEXER 74LS04 INVERTER 74LS >1 MULTIPLEXER 74LS08 2 INPUT AND 74LS >4 DECODER 74LS10 3 INPUT NAND 74LS > 1 MULTIPLEXER 74LS11 3 INPUT AND 74LS161 4 BIT COUNTER 74LS20 4 INPUT NAND 74LS163 4 BIT COUNTER 74LS25 4 INPUT NOR 74LS164 8 BIT SHIFT REG 74LS27 3 INPUT NOR 74LS169 4 BIT COUNTER 74LS30 8 INPUT NAND 74LS170 4 x 4 REGISTER 74LS32 2 INPUT OR 74LS174 HEX D F-F 74LS42 4-->10 DECODER 74LS175 QUAD D F-F 74LS74 DUAL D F-F 74LS191 4 BIT COUNTER 74LS75 QUAD LATCH 74LS193 4 BIT COUNTER 74LS83 4 BIT ADDER 74LS194 4 BIT SHIFT REG 74LS85 4 BIT COMPARATOR 74LS195 4 BIT SHIFT REG 74LS86 2 INPUT XOR 74LS244 OCTAL BUFFER 74LS93 4 BIT COUNTER 74LS259 8 BIT ADDER 74LS95 4 BIT SHIFT REG 74LS283 4 BIT ADDER 74LS109 DUAL J-K' F-F 74LS373 OCTAL LATCH 74LS >8 DECODER Table 1. - TTL Chip Inventory 8

9 TTL Quick Reference Fig TTL gates quick reference guide 9

10 VII. Circuit Testing and Input Generation and Output Display. Once the circuits for your lab experiment have been designed and built on your breadboard, the final step is to test them and verify that they produce the set of outputs expected for the set of inputs provided. The set of inputs to test your circuit can be generated in two different ways: manually and automatically. a). - Manual Generation and Display of Input and Output Variables To generate a logic variable manually, you can use the set of binary static switches or pushbuttons available from the Heathkit board, and to display these signals you can connect the set of input signals and the set of output signals to the logic indicator displays available also from the Heathkit board. In order to use one of the switches to generate a logic variable, just connect a wire to the breadboard output of the respective switch, and connect the other side of the wire to the respective input. To observe the state of this input you can connect another wire from this variable to one of the displays. b). - Automatic Generation and Display of Input and Output Variables To generate the sets of inputs and display the outputs on the oscilloscope screen automatically, you can use the Chipmonk circuitry and its connector (shown in Figure 15). This system produces four switching variables named W, X, Y and Z, and generates all possible combinations of values that these variables could have. This is, the values change from 0000 to 1111 and repeat continuously, with W been the most significant value, and Z the least significant value. W X Y Z Sequence Clock Column 8 Ground V cc Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Fig Chipmonk Connector The oscilloscope will show 16 rows of ones or zeros, and 8 columns. The screen displays one row for each combination of values, and each column represents a different variable, as shown in Figure 16. In order to display the value of a variable on the oscilloscope screen, just connect the variable of interest to the any of pins of the Chipmonk connector labeled Column 1 through Column 7 (pin numbers 15 through 9, respectively). Column 8 is special and should not be 10

11 used for testing combinational circuits. The use of this pin will be explained later in the sequential circuits section. When the Chipmonk is working correctly you should see displayed on the oscilloscope screen a truth table showing the input and output variables for your circuit. The variables will be displayed from left to right on the screen, in the same order that you wired them to the Chipmonk, as shown in Figure 16. Normally, when testing your experiments, you will want to display both the inputs to your circuit (W, X, Y, Z) and the outputs produced by your circuit, so that you can determine whether the proper output values are produced for each combination of input values. You can use any column to display either the value of an input or the value of an output. Col 1 Col 2 Col 3 Col 4 Col 5 Col 6 Col 7 Col 8 Fig. 16. Columns and Rows Displayed on the Oscilloscope Screen 11

12 In order for the Chipmonk circuitry and Oscilloscope to work properly, the Heathkit frequency and frequency multiplier knobs (3 & 4 on Fig. 1) should be set fully clockwise. The oscilloscope controls should all be set on the X-Y mode (1, 2, 3 and 4 in Fig. 17). Set channels 1 and 2 both at 0.5 volts per division (5, 6); AC coupled (7, 8), and pull out the channel 2-position control (9). Use the channel 2 position and the horizontal position adjustments to center the display on the screen. Once these controls are set, they should not need to be changed Fig. 17. Oscilloscope Controls Next, in the section VIII we show a table with the main Boolean Algebra laws, theorems and properties that can be applied to reduce a logic function. 12

13 VIII. - Basic Laws and Theorems for Boolean Algebra. IDENTITY LAWS X + 0= X X 1= X X + 1= 1 X 0= 0 IDEMPOTENT LAWS X + X = X X X = X INVOLUTION LAW (X')' = X COMPLEMENT LAWS X + X' = 1 X X' = 0 COMMUTATIVE LAWS X + Y = Y + X X Y = Y X ASSOCIATIVE LAWS (X + Y) + Z = X + (Y + Z) (X Y) Z = X (Y Z) DISTRIBUTIVE LAWS X(Y + Z) = X Y + X Z X + Y Z = (X + Y) (X + Z) SIMPLIFICATIVE THEOREMS X Y + X Y' = X (X + Y) (X + Y') = X (X + Y')Y = X Y X Y' + Y = X + Y ABSORPTION THEOREMS X + X Y = X X (X + Y) = X DEMORGAN'S LAWS (X + Y) ' = X' Y' (X Y) ' = X' + Y' X + X Y = X + Y X (X + Y) = X' Y 13