The Digital Circuit Construction Simulator with Virtual Scenarios and Interactive Tutorials is a program for building digital circuits on a virtual digital module using logic models of standard integrated circuits (TTL LS family and application-specific integrated circuits ASICs).
Circuits can be simulated directly on the digital module and, in some cases, validated with virtual scenarios that represent the environment in which the circuits will operate. Furthermore, the created circuits can be saved, retrieved, and edited.
The program also provides interactive tutorials for some typical logic circuits, many of which include VHDL descriptions. This software has been designed as a teaching and learning tool for digital design and is currently geared towards introductory courses in digital circuits, at both the school and university levels.
Advantages of the Program
Contents
It includes a large number of integrated circuit models from the TTL LS family.
The built circuits can be stored and retrieved. This allows for verification and reuse of examples in both teaching and learning digital design.
The tutorials next to the digital module allow for quick validation of acquired knowledge.
The scenarios provide a better perspective and facilitate a better initial specification of the logic design.
The ASICs simplify designs and save space on the breadboard, and can be used as examples of the desired circuits’ operation. This feature can be useful, for example, for teaching the partitioning of digital design. New ASIC models can be created from VHDL descriptions or C++ programs, but currently only at the programming level.
Limitations
The circuit models are based on TTL circuits with DIP packages. The user cannot create new models.
All models are purely logic-based, without three-state or bidirectional pins or ports.
The models do not account for electrical effects (signal propagation delays, input/output fan-out, noise, etc.).
The number of scenarios and tutorials is limited.
The Digital Module
The digital module (Figure 1) consists of the following elements:
A breadboard for wiring circuits
Electrical indicators: 18 single LEDs and 3 seven-segment displays
1Hz and 10Hz clocks
Digital inputs: 12 switches and 4 pushbuttons
Power supply: VCC and GND lines
18-line expander for connecting to a scenario
A main switch for turning the system on and off
Circuit Editing
Circuit editing is very simple. Chips are selected from a circuit category menu and then inserted into the breadboard. Wires are drawn by tracing lines with the mouse. Wires and chips can be removed by right-clicking on the chip or on one end of the wire.
Scenarios
Scenarios can be selected and inserted from the program menu. With the main switch off, the scenario operates in independent mode, following a predefined behavior. In this mode, the user observes how the circuit should interact with the environment or workspace. When the switch is turned on, the scenario responds to signals from the module.
Tutorials
The tutorials present the basics of some topics. In several cases, VHDL descriptions are included. More tutorials with improved pedagogical features will be included in a future version.
The current tutorials include basic gates (AND, OR, NOT), decoders (1-to-2, 1-to-4, 1-to-8, 74138), multiplexers (2-input, 2-input 4-bit, 74157, 4-input, 8-input, 74151), adders (full, 2-bit, 4-bit, 7483A), comparators (1-bit, 4-bit, 7485), latches (SR with NOR, SR with NAND), and flip-flops (74LS76A).
Standard Integrated Circuit Models
The following list shows the LS TTL integrated circuits modeled in this program:
Combinational Circuits
AND
7408 – 2-input AND (x4)
7411 – 3-input AND (x3)
7421 – 4-input AND (x2)
NAND
7400 – 2-input NAND (x4)
7410 – 3-input NAND (x3)
7420 – 4-input NAND (x2)
7430 – 8-input NAND
74133 – 13-input NAND
NOT
7404 – NOT (x6)
NOR
7402 – 2-input NOR (x4)
7427 – 3-input NOR (x3)
74260 – NOR
5-input (x2) OR
7432 – 2-input (x4) OR
7486 – 2-input (x4) XOR
74386 – 2-input (x4) XOR
AND – OR – INVERTER
7451 – 2-product, 2-3-input
7454 – 3-2-2-3-input
7455 – 2-product, 4-input
Encoders
74147 – Priority Encoder, 10 lines to 4
74148 – Priority Encoder, 8 lines to 3
Decoders
7442 – 10-line Decoder (BCD to Decimal)
7447 – BCD to 7-segment Decoder
74137 – 8-line Decoder/Demultiplexer
74138 – Decoder 8 lines
74139 – 1-to-4 line decoder/demultiplexer (x2)
74155 – 1-to-4 line decoder/demultiplexer (x2)
74247 – BCD to 7-segment decoder
Multiplexers
74151 – 8-to-1 line multiplexer
74153 – 4-to-1 line multiplexer (x2)
74157 – 2-to-1 line multiplexer (x4)
74158 – 2-to-1 line multiplexer (x4)
74298 – 2-to-1 line multiplexer with register (x4)
74352 – 4-to-1 line multiplexer (x2)
74398 – 2-to-1 line multiplexer with register (x4)
74399 – 2-to-1 line multiplexer 1 with register (x4)
ALU
74181 – 4-bit Arithmetic Logic Unit
Parity Generator
74280 – 9-bit Even/Odd Parity Generator/Checker
Comparer
7485 – 4-bit Magnitude Comparator
Adders
7483A – 4-bit Adder
74283 – 4-bit Adder
Sequential Circuits
Flipflops
7473A – Negative Edge JK Flipflop (x2)
7474A – Positive Edge D Flipflop (x2)
7476A – Negative Edge JK Flipflop (x2)
74107A – Negative Edge JK Flipflop (x2)
74109A – Positive Edge JK Flipflop (x2)
74112A – JK Flipflop negative edge (x2)
74113A – Flipflop JK negative edge (x2)
74114A – Flipflop JK negative edge (x2)
Records with Latches
7475 – 4 latches D
7477 – 4 latches D
74256 – 4-bit addressable latch (x2)
74259 – 8-bit addressable latch
74279 – 4 latches with set and reset
74375 – 4 latches D
Registrations with Flipflops
74174 – 6 D flipflops
74175 – 4 D flipflops
74273 – 8 D flipflops with clear
74377 – 8 D flipflops with enable
74378 – 6 D flipflops with enable
74379 – 4 D flip-flops with enable
Shift Registers
7495B – 4 bits
74164 – Serial input, parallel output
74165 – 8 bits, parallel to serial
74166 – Parallel input, serial output
74194A – Bidirectional, 4 bits
74195A – 4 bits, universal
Memory
74170 – 4 x 4 read/write memory
Asynchronous Counters
7490 – Divide by 2 and 5
7492 – Divide by 2 and 6
7493 – Divide by 2 and 8
74196 – Divide by 2 and 5
74197 – Divide by 2 and 8
74290 – Divide by 2 and 5
74293 – Divide by 2 and 8
74390 – Divide by 2 and 5 (x2)
74393 – 4-bit binary counter (x2)
74490 – Decade counter (x2)
Synchronous Counters
74160A – Module 10, asynchronous reset
74161A – Module 16, asynchronous reset
74162A – Module 10, synchronous reset
74163A – Module 16, synchronous reset
74168 – Bidirectional, module 10
74169 – Bidirectional, module 16
74190 – Module 10
74191 – Module 16
74192 – Bidirectional, BCD
74193 – Bidirectional, module 16
74669 – Bidirectional, module 16
NOTE: The bidirectional pin of the 7447 has been modeled as an output only.
Application-Specific Integrated Circuit Models
There are four ASIC models:
74801 (six-light traffic signal with day and night modes)
74802 (BCD counter with binary output and built-in 7-segment decoder)
74803 (counter from 0 to 8)
74804 (traffic signal with pedestrian sensors)
Author’s note: Let’s work for a better world. Take care. Warm greetings from Chincha, Peru.
Source: tourdigital.net
