ECET230_ilab procedure

Table 2.1 is the truth table for the 74LS157.

Table 2.1 – 74LS157 Truth Table (from focus.ti.com)

The chip select can be thought of as an on-off switch for the circuit. When this signal is HIGH, the chip ignores all other inputs and outputs logic LOW signals. Chip selects are useful in combining several chips, cascading, to perform various logic functions. multiplexer as shown in your textbook.

A seven-segment display is an array of seven bar-LEDs arranged to represent the decimal digits 0 to 9. To represent a digit, various segments (LEDs) are turned ON and OFF. The layout of the seven-segment display used in this lab is shown in Figure 2.1. Note that on some chip, the pins with No Connect do not exist.

Any of the digits 0 => 9 can be displayed using the seven segments (actually a small eighth segment is there for a decimal point). To display a “0”, we would turn OFF segment g and turn ON all the others. To display a “1”, b and c = ON and the rest OFF and so on.

Figure 2.1 – Common Anode Seven-Segment Display

This display is called a common anode type since the anodes (the positive sides, as opposed to the negative sides, which are call the cathodes) of the LEDs are connected together (pins 3, 9, 14) and tied to +5 volts. This means that a segment is turned on with a Logic 0 and turned off with a Logic 1. The common anode display is used more often than the common cathode because most logic devices can sink more current (Logic 0 output) than they can source (Logic 1 output). Note that the part in your kit will not have 14 pins since those connection marked “No Connect (NC)” have no physical pins.

PROCEDURE

A. Discrete Circuit Design

1. Using Multisim, create the schematic for the circuit shown in Figure 2.2. The schematic must be drawn before building the circuit.

Figure 2.2 – Multiplexer/Decoder Circuit (for Simulation)

2. Run various simulations to verify that the multiplexer is properly selecting the correct data inputs.

3. Build the circuit shown in Figure 2.3. The difference from the circuit in Figure 2.2 is that 330Ω resistors have been added between the decoder and the 7-segment display. Remember to wire the power and ground pins on the ICs.

Figure 2.3 – Multiplexer Circuit (for Discrete Hardware)

4. Set the upper set of switches (4A – 1A) to a value of 0101 and the lower set (4B – 1B) to 1001. Set the Data Select switch to a logic LOW. What number does the display show? Display = _________

5. Change the Data Select switch to a logic HIGH. Record the output. Display = __________

6. Photograph your final circuit for submission (online) or demonstrate your circuit to your professor (onsite or blended).

Instructor Sign-off ____________________

B. Design Project

1. Develop the VHDL code to create the multiplexer-decoder circuit shown in Figures 2.2 and 2.3 for the eSOC III board, download the code and submit the code and simulation to your instructor. Note that for the eSOC III board the resistors are not required and the seven-segment display must be driven by active-HIGH signals as shown in Figure 2.4.

( Binary-to- 7-Segment Decoder ) ( Q uad 2-to-1 Mux )