SimLog¬ is an application program for Macintosh computers that allows you to design and test basic digital logic theory through the use of a highly interactive simulation. With SimLog¬ it is easy to create complex logic circuits, to examine their static and dynamic behaviour and subsequently change and save your designs. This document assumes that the reader is adequately familiar with the standard Macintosh concepts of 'clicking', 'double-clicking', 'dragging', and 'selecting' using the mouse. It further assumes that you know how to manage files on discs, select from menus using both the mouse and the command keys and how to manipulate windows. See your Macintosh user guide for further information.
The Logic Simulator program SimLog¬ is a powerful teaching aid intended to accompany a taught course on Logic Design or Computer Architectures. It allows you to build complex logic circuits which can be tested, saved, modified and printed. It has a built-in logic simulator which is constantly active, reflecting every change that takes place in the circuit both on-screen and, for certain output devices, via an externally connected hardware mimic. A password systems controls access to certain higher features of SimLog¬ thereby allowing the tutor to structure the laboratory sessions. One very important aspect of SimLog¬ is the user interface which is highly interactive and intuitive to use, responding almost instantly to the directions. A sophisticated routing algorithm is incorporated which removes the overhead of detailed route planning for interconnecting wires and solves the problems of indistinct interconnections.
SimLog¬ is primarily configured to emulate TTL; (Transistor-Transistor-Logic) devices for which all unconnected logic inputs behave as a logic '1'. Fan-out (the number of inputs which can be driven from one output) for most gates is 10. Variable propagation delay has not been included but is considered to be equal through all logic elements. Both Synchronous and Asynchronous devices have been included and propagation race conditions will be displayed correctly. There are a range of input and output devices which can be configured to represent the electronic engineer's view of their operation or a simplistic view.
SimLog¬ has been developed after many years of running a Logic design course, which was a prerequisite to a Computer Systems course. It has always been felt that a good practical back-up to the taught course significantly aids the student's understanding of the principles involved. SimLog¬ represents the first product to appear from the Computer Aided Learning Initiative within the Department of Computer Studies at Loughborough University of Technology and has been successfully used in the undergraduate course at LUT for the past four years. It is accompanied by a detailed user manual and a password configuration facility - SimPass¬. Options include the provision of a structured laboratory course set and a Hardware Emulation Board (the application may be run without this unit).
Features:
SimLog¬ embodies a complex micro-world pertaining to Logic Design that can be freely explored by the student. Features are provided to aid the student in the construction of circuits from component parts and subsequently to evaluate the design. Some of the finer points of hardware behaviour are deliberately suppressed in order to make the educational aspects foremost.
The main features of SimLog¬ are:
A fully supportive file handler allowing storage and retrieval of complete or partial circuits.
A highly interactive graphic display on screen that can view up to four circuits at any one time.
Each circuit can be printed in full on a local or networked printer.
The standard Macintosh features of Copy and Scrapbook are available.
Logic devices supported include:
- Logic Gates: NAND, AND, NOR, OR, XOR and NOT.
- D-type flip-flops
- Decoders and Drivers
- Counters
- Tri-State TRUE and INVERTING Buffers, Tri-State Latches
- Shift registers
- Memories
- Adders, Arithmetic and Logic Units.
Input and Output devices supported:
- Basic Toggle and Push Switches
- Oscillators
- Numeric and Hexadecimal Keypads
- A Random Number Generator
- LEDs
- Traffic Light Displays
- Seven Segment Displays
- Bells
- Multi-Character Alpha Numeric (ASCII) Displays.
- Uncommitted Outputs;
Simple devices such as the basic gates may be obtained in a variety of sizes (1,2,3,4 and 8 input) and may be oriented in any of the four prime directions.
Basic Switches and LEDs may be viewed as block diagrams or in electronic engineering notation.
Connections are made from point to point using the mouse. The wiring is automatically routed and drawn by the system. The connection is maintained during Subsequent moves of the logic element on screen.
Where bus connections are required the user need only make a single connection and the rest will be done automatically.
Networks of connections are supported and may be built and dismantled at will.
Up to twenty oscilloscope probes (simulated) may be attached to each circuit and an oscilloscope window used to display dynamic or stored timing diagrams. Certain educational points have been carefully exploited:
All Logic and I/O devices have explicit pictorial representations to aid recognition and understanding.
Truth tables may be summoned on-line at any time.
Every circuit, device, input and output may be independently named. Circuit and device names appear on screen. They are automatically and uniquely named on creation but may be altered by the student.
All input and output connections to the devices are clearly visible and reflect the state of the connection ('1', '0', tri-state, unconnected or destroyed).
Unconnected inputs behave in a clear and noise free manner.
Illegal connections between active and opposite outputs result in the destruction of the logic device.
All input devices may be operated by using the mouse during the simulation. Oscillators may be set to run continuously.
Multiple oscillators may be run in synchronous or asynchronous modes. Each has an independently adjustable period and mark-to-space ratio. Each can be set to on or off.
Where the simulation occurs too rapidly to observe the effect in real time (eg., in a counter reset loop) the simulation can be set to single step, allowing the observer to note the input and output states at each phase.
Some of the output devices (LED types and uncommitted outputs) may be directed to the Emulation board which mimics the on screen behaviour. The uncommitted outputs may be further connected to any TTL compatible input.
The copy of SimLog¬ that you have obtained (either by disc or network) is intended to be freely copied and distributed. It is intended to provide a demonstration of the full version, of which further details can be obtained from Oxford University Press. Whilst many of the significant features of the constructional user interface have been removed (for copyright reasons) the selection of demonstration circuits bundled with this copy should give you a full insight into the potential of SimLog¬ as a learning aid.
As a further precaution against misuse, the program will only allow between 15 and 20 minutes of use before closing down unexpectedly.
