1. Lecture #8 EGR 277 – Digital Logic
Reading Assignment: Chapter 4 in Digital Design, 3rd Edition by Mano
BCD-to-7-segment decoder/driver
This is a special type of decoder that is used to drive a 7-segment display.
There are two types of 7-segment displays using LED’s:
1) common anode (all anodes at +5V)
2) common cathode (all cathodes at ground)
If a common-cathode display is used (as shown below) and if the decoder outputs a HIGH on output a, then segment a will be lit. Note that “current-limiting resistors” are required for each segment or else the segment may be destroyed due to excessive current. The 7448 is a commercially available BCD-to-7-segment decoder/driver with active-HIGH outputs so it is intended to drive a common-cathode display.

2. Lecture #8 EGR 277 – Digital Logic
Similarly, a common-anode display requires a driver with active-LOW outputs, such as the 7447.
Develop a truth table for designing a BCD-to-7-segment decoder driver.

3. Lecture #8 EGR 277 – Digital Logic
PSPICE Analysis of Digital Circuits
In EGR PSPICE was used to analyze various types of circuits. Several methods of analysis were used, including:
Bias Point Analysis
DC Sweep
AC Sweep
Transient
Parametric
Analysis of logic circuits will only involve transient analysis - in order to generate timing diagrams to show outputs for various combinations of inputs.
Full version of PSPICE: One of the strengths of the full version of PSPICE is that it includes libraries for tens of thousands of components.
Evaluation version of PSPICE: The evaluation version contains a few hundred devices, most of which are 7400 series TTL devices. This is very useful for this course and allows students to analyze circuits using devices that are pin-for-pin compatible with those covered in the text and in lab.

4. Lecture #8 EGR 277 – Digital Logic
7400 Series parts found in the evaluation library (eval.slb):
7400 Quadruple 2-input Positive-Nand Gates
7401 Quadruple 2-input Positive-Nand Gates with Open-Collector Outputs
7402 Quadruple 2-input Positive-Nor Gates
7403 Quadruple 2-input Positive-Nand Gates with Open-Collector Outputs
7404 Hex Inverters
7405 Hex Inverters with Open-Collector Outputs
7406 Hex Inverter Buffers/Drivers with Open-Collector High-Voltage Outputs
7407 Hex Buffers/Drivers with Open-Collector High-Voltage Outputs
7408 Quadruple 2-input Positive-And Gates
7409 Quadruple 2-input Positive-And Gates with Open-Collector Outputs
7410 Triple 3-input Positive-Nand Gates
7411 Triple 3-input Positive-And Gates
7412 Triple 3-input Positive-Nand Gates with Open-Collector Outputs
7413 Dual 4-input Positive-Nand Schmitt Triggers
7414 Hex Schmitt-Trigger Inverters
7416 Hex Inverter Buffers/Drivers with Open-Collector High-Voltage Outputs
7417 Hex Buffers/Drivers with Open-Collector High-Voltage Outputs
7420 Dual 4-input Positive-Nand Gates
7422 Dual 4-input Positive-Nand Gates with Open-Collector Outputs

5. Lecture #8 EGR 277 – Digital Logic
7400 Series parts found in the evaluation library (eval.slb):
7423 Dual 4-input Nor Gates with Strobe
7425 Dual 4-input Nor Gates with Strobe
7426 High-Voltage Interface Positive-Nand Gates
7427 Triple 3-input Positive-Nor Gates
7428 Quadruple 2-input Positive-Nor Buffers
input Positive-Nand Gates
7432 Quadruple 2-input Positive-Or Gates
7433 Quadruple 2-input Positive-Nor Buffers w/ Open-Collector Outputs
7437 Quadruple 2-input Positive-Nand Buffers
7438 Quadruple 2-input Positive-Nand Buffers w/ Open-Collector Outputs
7439 Quadruple 2-input Positive Nand Buffers with Open-Collector Outputs
7440 Dual 4-input Positive-Nand Buffers
7442A DECODER BCD-DECIMAL 4-10 LINE
7443A DECODER EXCESS-3-DECIMAL 4-10 LINE
7444A DECODER GRAY-DECIMAL 4-10 LINE
7445 DECODER/DRIVER BCD-DECIMAL WITH OPEN COLLECTOR OUTPUTS
7446A DECODER/DRIVER BCD-7 SEGMENT WITH OPEN-COLLECTOR OUTPUTS
7447A DECODER/DRIVER BCD-7 SEGMENT WITH OPEN COLLECTOR OUTPUTS

6. Lecture #8 EGR 277 – Digital Logic
7400 Series parts found in the evaluation library (eval.slb):
7448 DECODER/DRIVER BCD-7 SEGMENT WITH INTERNAL PULLUPS
7449 DECODER/DRIVER BCD-7 SEGMENT WITH OPEN-COLLECTOR OUTPUTS
7450 Dual 2-wide 2-input And-Or-Invert Gates
7451 And-Or-Invert Gates
7453 Expandable 4-wide And-Or-Invert Gates
wide And-Or-Invert Gates
7460 Dual 4-input Expanders
7470 And-Gated J-K Positive-Edge-Triggered Flip-Flops with Preset & Clear
7472 And Gated J-K Master-Slave Flip-Flops with Preset and Clear
7473 Dual J-K Flip-Flops with Clear
7474 Dual D-Type Positive-Edge-Triggered Flip-Flops with Preset and Clear
bit bistable latches (dual 2-bit common clock4-bit bistable latches )
7476 Dual J-K Flip-Flops with Preset and Clear
bit bistable latches
BIT BINARY FULL ADDERS
7483A 4-BIT BINARY FULL ADDERS WITH FAST CARRY
BIT MAGNITUDE COMPARATOR
7486 Quadruple 2-input Exclusive-Or Gates

7. Lecture #8 EGR 277 – Digital Logic
7400 Series parts found in the evaluation library (eval.slb):
7490A COUNTER DECADE 4-BIT, ASYNCHRONOUS
7491A 8-BIT SHIFT REGISTERS
7492A COUNTER DIVIDE-BY-12 4-BIT, ASYNCHRONOUS
7493A COUNTER BINARY 4-BIT, ASYNCHRONOUS
BIT SHIFT REGISTERS
7495A 4-BIT PARALLEL SHIFT REGISTERS
BIT PARALLEL-OUT SERIAL SHIFT REGISTERS
Bit Bistable Latches
Dual J-K Flip-Flops with Clear
Dual J-KBar Positive-Edge-Triggered Flip-Flops w/ Preset & Clear
And-Gated J-K Master-Slave Flip-Flops with Data Lockout
Dual J-K Master-Slave Flip-Flops with Data Lockout
Non-retriggerable Monostable Multivibrator w/Schmitt-Trigger Inputs
Retriggerable Monostable Multivibrator
Retriggerable Monostable Multivibrator
Quadruple Bus Buffer with 3-state Outputs
Quadruple Bus Buffer with 3-state Outputs
Line Drivers
Quadruple 2-input Positive-Nand Schmitt Triggers

8. Lecture #8 EGR 277 – Digital Logic
7400 Series parts found in the evaluation library (eval.slb):
Quadruple 2-input Exclusive-Or Gates with Open-Collector Outputs
DECODER/DRIVER BCD-DECIMAL WITH OPEN COLLECTOR OUTPUTS
PRIORITY ENCODER 10-4 LINE
PRIORITY ENCODER 8-3 LINE
74151A MULTIPLEXER/DATA SELECTOR 8-1 LINE
DECODER/DEMULTIPLEXER 4-16 LINE
DECODER/DEMULTIPLEXER 2-4 LINE
DECODER/DEMULTIPLEXER 2-4 LINE WITH OPEN COLLECTOR OUTPUTS
QUADRUPLE 2-LINE TO 1-LINE DATA SELECTORS/MULTIPLEXERS
DECODER/DEMULTIPLEXER 4-16 LINE WITH OPEN COLLECTOR OUTPUTS
Synchronous 4-bit Decade Counters with asynchronous clear
Synchronous 4-bit Binary Counter with Direct Clear
Synchronous 4-bit Decade Counters with synchronous clear
Synchronous 4-bit Binary Counter
BIT PARALLEL-OUT SERIAL SHIFT REGISTERS
REGISTERS D-TYPE 4-BIT WITH 3-STATE OUTPUTS
HEX D-TYPE FLIP-FLOPS WITH CLEAR
QUADRUPLE D-TYPE FLIP-FLOPS WITH CLEAR
etc.

9. Lecture #8 EGR 277 – Digital Logic
New Parts: The following parts will be introduced:
1) DIGITAL CLOCK – located in the library named SOURCE.OLB
Note that the OFFTIME and the ONTIME can be set to produce a waveform with the desired period. For example, the Digital Clock below has a period of 2ms.
T = 2ms
Similarly, three Digital Clocks could be used to generate waveforms A, B, and C representing the 8 possible input combinations. Since the period of the MSB is 8ms, a transient analysis of 8ms could be used to test circuit outputs for all 8 input combinations.
T = 4ms
T = 2ms
T = 8ms
Count (ABC): A B C

10. Lecture #8 EGR 277 – Digital Logic
2) HI and LO inputs – located in the library named SOURCE.OLB
Note that a ground is not used in digital circuits and HI and LOW inputs must be produced using these inputs (5V and GROUND will not work).
3) Series TTL devices – located in the library named EVAL.OLB
The EVAL library contains a wide assortment of 7400 series devices. In general, they are pin-for-pin compatible with commercially available devices. For simple logic gates, such as the 7400 NAND, 7402 NOR, 7404 NOT, etc., single gates are inserted rather than an entire IC (a 7400 NAND contains 4 2-input NAND’s). More complex devices match the IC’s exactly. Some examples are shown below.

11. Lecture #8 EGR 277 – Digital Logic
Demonstration: Use ORCAD to demonstrate how to implement a Boolean expression:
1) in SOP form using AND, OR, and NOT gates
2) using a 3x8 decoder