e991x11.pdf

New software to simulate logic circuits seems to hit

the streets every month, and most of you will be

aware that logic simulation on a PC is a good alter-

native to wiring up prototypes of digital circuits.

By J.P. Strzalka

Logic Simulator 2.0

First prize, France

allows you to actually launch Simulat.

To do so, double-click on this icon with

the left-hand mouse button. In this way

you start the simulator program.

Schematic capture

The program enables you to create cir-

cuit diagrams. For this function it offers

a number of tools that allow users to

include elementary logic elements like

gates, flip-flops, adders, multiplexers,

demultiplexers, timers or counters in

your schematic. A rather complex

example of such a circuit is shown by

the screendump in Figure 1 . This is

actually a counter circuit.

Simulation program

The logic simulation program ‘Simulat

2.0’ was awarded the First National

Prize for Competition entries sent to our

French editorial department. The pro-

gram is aimed at students, teachers

and hobbyists wishing to widen their

knowledge of sequential and combi-

natory logic circuit design.

Simulat 2.0 allows you to draw

schematics of logic circuits in a win-

dow displayed on your PC monitor.

Once you think the schematic is com-

plete, you launch a simulation run

using virtual switches, displays or other

indicators and devices to control and

visualize the way the logic circuit oper-

ates (or not!). Simulat 2.0 is capable of

handling four schematics at a time.

Program installation

The program is easy to install under the

Windows 95 operating system.

Select ‘Run’ from the Start menu, type

‘X:\setup’, and then press the Return

key, where ‘X:’ is the letter of the drive

station that has the ‘setup’ file.

Alternatively, use the ‘Browse’ option to

get assistance from Windows 95 in

looking for the setup program. If you

use the Elektor CD-ROM which con-

tains the present project, navigate to

the subdirectory /F/01 where you will

find setup.exe.

The installation program builds a

group of three programs. The group is

called ‘Simulat’, and it will contain

three icons. The first icon in the group

The ‘pencil’ tool allows you to connect

logic gates. Only right angles are pos-

sible for the ‘wires’. To use the pencil,

pick it from the Tools bar, and left-click

on an input or output of a logic oper-

ator. Next, move the mouse to the

operator you want to connect up, and

then release the mouse button.

The ‘Copy’ utility of Simulat also sup-

ports the use of the Clipboard to cut,

copy, delete and paste elements in

your circuit diagram.

Simulat has deletion utilities: for logic

operators, connections and junctions.

To delete an object, select the corre-

sponding utility from the Tool bar.

The schematic may be spiced up a bit

by text with or without a frame. It is pos-

sible to choose fonts, colours and

character sizes, as well as text orienta-

tion (vertical or horizontal). The user

may choose the frame colour, shade

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test all connections and display its

findings as the test progresses. Any

error encountered in this process, is

made known to you by means of dia-

logue boxes. If Simulat does not

encounter errors, it is possible to oper-

ate the virtual switches, indicator

lamps, displays and thumbwheel

switches, and so set up and manipu-

late various conditions to which the vir-

tual logic circuit responds.

The links in the circuit diagram are

shown in different colours depending

on their logic level. You can read the

logic level of an operator by left-click-

ing on the operator input or output.

The cursor will then change to a sym-

bol indicating ‘zero’ or ‘one’.

Simulat 2.0 also comes with a logic

oscilloscope capable of displaying up

to five signals taken from points you

indicate in the circuit diagram. The

oscilloscope is ‘triggered’ by either a

rising or a falling pulse edge detected

on one of the five input channels. If the

oscilloscope trace is not stable, you

may insert a trigger delay to keep this

virtual instrument synchronized.

Oscilloscope traces may be copied

onto the Clipboard, or saved in a file.

Furthermore, scope traces may be

sent to the printer to produce hard

copy, at a scaling factor you select.

Alternatively, Simulat can compute the

scale value needed to adapt the size

of the drawing to that of the paper in

the printer.

etc.). Equations may be saved on the

Clipboard or in a file on your disk. It is

also possible to compute a partial

equation. To do so, you click on the

corresponding button shown by the

dialogue box. Simulat then temporari-

ly closes the box to enable you to click

on the desired logic gate. Once that is

and the frame type. Frame size is auto-

matically adjusted to the amount of

text and character height selected by

the user.

It is possible to write up some com-

ment with each schematic. The length

of the comment text is limited to 50

characters.

Tools

done, the dialogue box pops up

again on the screen, showing the

logic equation against a red back-

ground.

The panoply of utilities found in the

working subdirectory is complement-

ed by a powerful ‘special logic’ cal-

culator which is capable of perform-

ing special functions like number con-

versions and shift-right /shift-left opera-

Library

Circuit elements may be saved in

order to build a library of basic build-

ing blocks.

To do so, you choose the option

‘Copy’ and then limit the selection to

the desired elements by means of a

dashed box. Next, you actuate the

command ‘save model to disk’ which

may be found in the menu called

‘Library’.

Finally, you may select the command

‘Load model from memory’. This caus-

es a certain element to be retrieved

from the library and placed at the

desired location in the current window.

tions. Using binary number notation,

the range of operands is adjustable

from eight bits to double 32-bit words.

In addition, a truth table is available to

help you remember the function of the

main logic operators. This useful little

tool pops up on the screen if you

select the corresponding command. A

simple mouse click on one of the logic

operator types in the scroll list instantly

displays the associated truth table and

the corresponding logic symbol.

Utilities & button palettes

Logic equations

The palettes (bars) containing utilities

and buttons allow you to change the

appearance of the program on the

PC screen. Modifying the utilities

palette allows you to increase the

actually visible area in the window

containing the schematic you are

working on. In this way, you will be

able to see more of your schematic.

These palettes may be moved around

to any location you want on the

screen. Furthermore, the palettes and

toolbars may be ‘hidden’ to create

even more space on the screen.

Simulat allows you to determine logic

equations based on a schematic.

The calculation box identified as

‘Equations’ allows you to print equa-

tions that belong with a circuit dia-

gram, using a number of options (line

spacing, separation, page number,

Circuit simulation

Having drawn and saved your

schematic, you are ready to launch

the circuit simulator. The program will

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Printing

sibilities for copying, moving, loading,

opening and deleting your schemat-

ics. It also supports displaying file

properties of disk drives, and free

space on the hard disk.

they are integrated into the file), while

linked objects remain stored in the

original (source) file. The schematic

then only keeps information relating to

the location of the object in the source

file.

Circuit diagram files may be selected

and moved into the simulation win-

dow. Using the file management sys-

tem you may pick one or more

schematics and drop them in the sim-

ulation window. Once the cursor is on

the program window, release the

mouse button, and the selected files

are loaded into the simulator. Note

that Simulat 2.0 can only handle four

schematics at a time.

Simulat 2.0 can provide a Print

Preview. This dialogue box allows you

to select the printable area, the scale,

page margins, contents of the ID box,

and other printer configurations,

Miscellaneous matters

Because Simulat 2.0 runs under the

Windows 95 operating system, you are

able to copy complete screens into

the Clipboard, and from there move

them to other applications like MS

Write, etc., in order to create docu-

ments (useful for educational/didactic

purposes).

Simulat 2.0 supports the Multiple

Document (MD) system. The program

allows you to work on four circuit dia-

grams simultaneously. The names of

the schematics are displayed in the

‘Window’ menu (‘Fenetre’). You can

change between circuit diagrams in

three ways:

- by left-clicking anywhere in the win-

dow of the schematic to be activated;

- by clicking on the name of the

schematic as listed in the ‘Window’

menu;

- by selecting the ‘Next’ option from

the System menu in a window.

System requirements

You will need to have Windows 95

installed (or a later version). The PC

should have a 386 processor or better,

4 Mbytes of RAM, a VGA card and a

mouse. Simulat 2.0 requires about

6 Mbytes of free space on your hard

disk.

before the print job is started.

The buttons in the dialogue box are

‘repeat’ types, allowing the relevant

command to be issued again by

keeping the cursor on the button rep-

resenting the desired command.

Compatibility is assured with any print-

er already functioning in graphics

mode, and driven by other applica-

tions running under Windows.

To print an ID box with the schematic,

click on the button ‘Cartouche’. A dia-

logue box pops up which allows you to

define the text fields which are to

appear in the ID box.

Paper margins may be set in the dia-

logue box ‘Page Setup’ (‘Mise en

Page’). In the title bar the program dis-

play the paper dimensions and the

printable area. These two values will of

course depend on the printer you

have connected up to your PC.

Note: The version described here supports

a maximum of 100 components. The

author can supply a larger version.

Simulat 2.0 also supports the OLE 2.0

system. The linking and embedding

functions allow Simulat 2.0 to accept

different data types and objects pro-

duced with other programs. The main

difference between linking an object

and embedding it concerns the way

in which data is stored: embedded

objects form part of a schematic (i.e.,

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Help system

A powerful, context-sensitive help sys-

tem is available.

To get help, you click on the

‘Contextual Help’ symbol in the button

bar. Next, you click your way through

the Help menu to get to the item you

need help on.

File management

The file management system allows

you to stay organized as far as your

schematics are concerned.

The system offers you a number of pos-

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