[editor : Carl T. Helmers Jr.] [publisher : Virginia Londoner (Virginia Londner), Gordon R Williamson] [art : Ellen Bingham, Wai Chiu Li, Christine Dixon, Nancy Estle] [cover : Robert Tinney] #Magazine
#Abstract
This issue's theme is provided by an article on various cartographic projections by William Johnston. To emphasize this theme of mapping terrain with computer models, Robert Tinney's painting "Beneath The Grid" shows a landscape with a superimposed grid of luminescent white lines as might be projected in the mind's eye by an appropriate graphic output device.
Microcomputers allow the quick and easy performance of operations that take an extemely long time to perform by hand. One of these operations is drawing maps from accumulated tables of data. William Johnston describes the simple programs used to produce Computer Generated Maps. page 10
A data tablet is a graphical input device that enables you to enter visual images into your computer. Richard Blum has a program for Representing Three·Dimensional Objects in Your Computer. page 14
If you need to communicate digital information from one point to another through an electrically noisy environment, then optical communications may be one solution. If you are going to communicate over long distances or at high speeds, then a laser may be the best choice for a light source. This month Steve Ciarcia explains how to Communicate on a light Beam. page 32
The people interested in just wetting their feet in the field of microcomputers are usually not looking for a very big system. A single board computer is often a good first experience. The Ohio Scientific Superboard II is one single board computer which has some interesting capabilities. Find out what Chris Morgan thinks about The Superboard II. page 50
Flexible video displays have been made possible by special display controllers. Bob Haas describes four devices from different manufacturers and tells how he used a specific video display controller in a successful construction project. You can learn more about these single integrated circuit marvels in Single Chip Video Controller. page 52
If you do not have documentation for a machine language program, it is almost impossible to determine how the program works. Bob Lentz describes a 6800 Disassembler that he wrote for his SwTPC 6800 system. page 104
Possession of an integer arithmetic language does not preclude the writing of intricate programs involving trigonometric functions. David J Beard describes how he used an integer BASIC to develop navigation routines for Spacewar in Tiny BASIC. page 110
The most prevalent form of output from a personal computer seems to be a video display. Therefore, the serious hobbyist should be aware of the number of different video display controllers that are available. Chris Tennant looked at the Intel 8275 video display controller and liked what he saw. In his article he describes a video interface using The Intel 8275 CRT Controller. page 130
In part 2 of Smart Memory, Randy Smith presents a series of black box diagrams to describe the workings of an associative memory. page 150
The "wraparound" queue can save you time during input and output operations on your computer. W D Maurer explains how the queue works and how to implement it on 8080 computer systems in Simultaneous Input and Output for Your 8080. page 164
Last month Len Gorney described how to implement a queue on a computer. This month he talks about real life queues and how the science of Queuing Theory can be applied. page 176
The CORDIC algorithm is a venerable and efficient method for calculating trigonometric functions. John A Ball gives some practical suggestions to experimenters in Trigonometry in Two Easy Black Boxes. Find out how you can streamline your number crunching with CORDIC. page 184
Good programming techniques are vital in personal computing as well as in computing in general. Author Delmer D Hinrichs, using tic-tac-toe as an example, describes the strategies of the game programmer in Tic·Tac·Toe: A Programming Exercise. page 196
Ralph Stirling describes how to turn a motorized wire wrap tool into a motorized unwrapping tool in The Hobby Unwrap. page 218
For owners of Signetics 2650 based computer systems, Edward R Teja and Gary Gonnella have provided a useful disassembler program to help make sense of those hexadecimal machine language listings. Read A Mini-Disassembler for the 2650. page 233
If your microcomputer lacks an assembler or high level language, it will be necessary to hand assemble all of your programs. To do this quickly and accurately it is a good idea to develop a consistent routine. Erich Pfeiffer describes a useful technique in Aids for Hand Assembling Programs. page 238
[author : Carl Helmers] #Edito
Extract : « With respect to manufactured products for the small computer user, we live in a time of plenty. There are at least 20 to 30 different manufactured or kit versions of complete personal computer systems, many featuring numerous models and sets of options. The hardware of these computers is complete, and in the better brands comes with ample documentation of the system's internals. The systems software comes in various stages of completeness and usefulness as a software development tool to satisfy particular personal computer users' needs.
Many readers, like myself, may tend to hesitate at the thought of experiments which involve building hardware to couple with appropriate software, in order to accomplish an application. But what is the mystery of peripheral hardware? [...] »
TABLE OF CONTENTS
Maps help make the arrangement of numeric data meaningful
[author : William D Johnston] #Algorithm #Listing #BASIC #Cartography
Extract : « Cartography, the art of mapmaking, originated in ancient times. It came of age in 1538 when Gerhard Mercator revolutionized the science with the introduction of the first modern mathematically derived map projections. Those projections, which bear his name, have stood the test of four and a half centuries, and to this day are of great value in a wide variety of applications. Many of the world's most famous cartographers lived, worked, and made great theoretical contributions more than 200 years ago. The names of Lambert, Mollweide, Lagrange, Gauss, and others will ring familiar to even the casual user of maps.
While these men all had brilliant minds, they shared an extraordinary handicap: that which they could conceive in theory they could put in practice only through enormous labor in manual computation. The construction of maps through mathematical projections begins with sets of geographical coordinates which define the boundaries of the areas to be mapped. These coordinates are manipulated with appropriate mathematical procedures to convert the geographical data to map coordinates, and these final numeric figures arc used to draw the maps. In practice, accurate maps require defining literally tens of thousands, and frequently hundreds of thousands — or even millions — of reference points. [...] »
Using a digitizer to input graphical data
[author : Richard Blum] #Listing #BASIC #DataAcquisition
Extract : « How would you like to make still pictures "come to life"? Or perhaps draw or photograph objects and then animate them, on a video display? You can do it on your personal computer with the help of a data tablet and the program described herein. The program takes images from a data tablet and transforms them into a three-dimensional representation inside a computer.
Once a three-dimensional representation of an object is entered into a computer's memory, programs can be used to display the object in perspective on a graphical video display. The object can be displayed from an infinite variety of perspectives. One can look at objects from any desired viewpoint and generate different viewpoints rapidly — a capability that is very useful in animation. [...] »
Transmit digital Information over a beam of light
[author : Steve Ciarcia] #Electronic #Networks #HowItWorks
Extract : « Coming up out of the Circuit Cellar is a rare occurrence, to the point where some of my friends have accused me of being a mushroom. I prefer to be likened to a mole—a more dignified species. We share a common bond of subterranean existence and fear of bright sunlight, but the mole's predicament is dictated by nature, and mine by choice.
The Circuit Cellar is by no means a hole in the ground. It's heated, well-lit and looks more like a living room than a cellar. Even though it affords all the comforts of home, there are those occasions when a change of environment is required. It's not enough to walk out in the driveway, take a deep breath and run back into the cellar. Sometimes a complete change of surroundings is needed to shock the mind out of the doldrums and spark creativity (eg: a vacation). Since I usually don't have time for vacations, I take "business excursions for purposes of cerebral detoxification" or "ECDs" for short.
For two months I had been wrestling with the details of an article on fiber optics and laser communications (this one). The hardware was completed very quickly, as with most of my projects, but the text dragged on for weeks. Lighting the wood stove in the Circuit Cellar became an all too easy chore using the piles of scrap paper I was generating. My graphospasms (ie: writer's cramps) were not bearing fruit. One time I even found myself sitting at my desk pushing pencils through the electric pencil sharpener until it started smoking. [...] »
Controlling a video display with a single Integrated circuit
[author : Bob Haas] #Display #Electronic #Listing #Assembly
Extract : « Several semiconductor manufacturers have recently produced video display controllers contained on a single integrated circuit. While none of these is the "video terminal-on-a-chip" that some of the publicity would have you believe, these new devices perform many of the functions required in a video display, thereby reducing the number of integrated circuit packages required. In addition, they are all programmable to some degree, which allows adding new features to an existing design at low incremental cost, or changing display formats if required by changing needs. These characteristics make these devices particularly interesting to a computer experimenter. A user might start with a 16 line, 64 character, upper case only display, and as requirements (and budget) increase, convert to a "professional" 24 line, 80 character, upper and lower case format just by adding more memory and a new character generator.
In this article, I will present a survey of the characteristics of four video display controllers, namely, the Intel 8275, the Motorola MC6845, the NS (National Semiconductor) DP8350, and the SMC (Standard Microsystems Corporation) 5027. In addition, I will present a detailed description of the Motorola part and a design for a display using that device. [...] »
This controller device eases video display design
[author : Chris Tennant] #Display #Electronic #Microprocessor #Review
Extract : « The Intel 8275 is a programmable video display controller manufactured by Intel Corporation. It is sealed in a 40 pin dual in line package. The device is presently expensive, but it replaces more costly circuitry of a greater size and complexity.
The 8275 has full color capability, a light pen option, many display modes, and simplicity in both hardware and software. This article's focus is on the ability and overall value of an 8275 based video terminal. Since value is a relative judgment, frequent comparisons will be made between an 8275 based terminal and other kinds of terminals presently available. [...] »
This single board computer can be expanded to a full-scale system
[author : Chris Morgan] #ComputerDesktop #Review
Extract : « My first experience with an Ohio Scientific product (in fact, my first experience with a personal computer) was with an OSI single board computer I bought in 1976. The unit sold for $99 and featured a row of eight switches and accompanying LEDs (light emitting diodes) for entering machine language programs. It had 256 bytes of programmable memory, and no other I/O (input/output) besides the LEDs. [...] »
Decipher your machine code programs
[author : Bob Lentz] #Listing #Assembly #Programming
Extract : « After spending two frustrating days trying to use MIKBUG to interface both a video display and a Teletype to the Southwest Technical Products SwTPC 6800 assembler (object code only), I wrote the disassembler in listing 1 to help me decipher the assembler. The disassembler and the program to be disassembled must be coresident in memory; the disassembler is located in the highest 2 K bytes of an 8 K byte memory, allowing it to operate on object programs up to 6 K bytes long. Temporary storage registers and the stack are located in the MIKBUG programmable memory area, hexadecimal addresses A000 thru A07F, and no page zero direct instructions are used. [...] »
A space navigation application
[author : David J Beard] #Listing #BASIC #Simulation
Extract : « So you want to fly your own spaceship, but you're not up to doing six months worth of assembly language programming and the only high level language you've got is a tiny version limited to 4 function integer arithmetic? That rules out any kind of realistic navigation — or so it seems. All digital machines are limited to integer mathematics. Nearly any operation possible in machine code can be duplicated in a high level language, provided you have enough memory and the time to wait for the results. Armed with a little bit of knowledge, though, you can keep the convenience of your interpreter and have three-dimensional trigonometry, too. Here's how I did it.
My first objective in writing a spacewar game was to provide a realistic trainer for spaceflight rather than a flashy video display or a complex set of board game type rules. I feel strongly that a spacewar game ought to be three-dimensional. The third dimension is far more than a frill: it's the major difference between spaceflight and surface operations. I developed the scenario for my game in 1972 when I was working with a homebrew analog computer. In my version a single ship maneuvers in Cartesian space and is attacked by a series of homing torpedos that must be either destroyed or evaded. The game requires both aimed laser fire and navigation precise enough to permit evasion by narrow margins.
This article describes the trigonometry routines developed for the game. It assumes that you are familiar with high school physics and right angle trigonometry. These routines represent a compromise between precision and speed; they are neither quick nor simple, but then, neither is astrogation. [...] »
A black box approach to associative memory design
[author : Randy C Smith] #Memory #Electronic #HowItWorks
Extract : « [...] The second and concluding part of this article reiterates these themes through the use of successive black box logic diagrams. No attempt is made to specify exact devices (as in a schematic), since the idea is to illustrate a general architecture. Once the conceptual components are understood (and this is only one of many forms for associative memories) the personal computer enthusiast can experiment with methods for further logic reduction through the use of large scale integration circuits, addition of circuitry for random access or multidimensional addressing, or even the application of more hardware processing power at each memory node. [...] »
A roundabout method of I/O
[author : W D Maurer] #Interface #Listing #Assembly
Extract : « The process of I/O (input/output) in assembly language on a typical microcomputer system is rather crude. You input the status register and perform a logical AND with a mask consisting of one bit. If the result is not zero, you know the bit was on and the I/O device was therefore ready. In that case, you either input or output the data register, as appropriate. Otherwise, you loop back to input the status register again. [...] »
Looking at realistic situations
[author : Len Gorney] #Method #Listing #BASIC #Book
Extract : « In part 1 we discussed the computer implementation of row and circular queues. Now, let us take a look at the structure of queues in the real world and see if they can be fitted to our previous programs. In the following discussion, the word queue refers to the waiting line in the system. The word facility refers to the service facility area located at the head of the queue.
System Types
There are four general types of queuing structures. The first, and simplest, is the single queue single facility system (figure 3). In this structure, there is one waiting line and one service area to be studied. A 1 pump gas station with one entrance is a real world example of this system. [...] »
Calculate trigonometric functions using arithmetic operations
[author : John A Ball] #Mathematics #Listing #BASIC #Book
Extract : « If your computer can add, subtract, multiply, divide, calculate square roots, sines, cosines, tangents, arc sines, arc cosines, and arc tangents, then you are prepared to solve any trigonometry problem. However, if your computer lacks some of these trig functions, then this article will be helpful, as it shows how to use CORDIC techniques to program two "black boxes" (alias subroutines or processors) to perform trigonometric functions. As a bonus, you will find that some complex and important problems are easier with the two black boxes than with conventional trig functions. [...] »
How to approach a programming task
[author : Delmer D Hinrichs] #GameBoard #Listing #BASIC
Extract : « Computer and calculator games serve at least four useful functions: Developing logic and mathematical skills. Demonstrating programming methods. Demonstrating operation of the computer. Providing entertainment. Keeping these possibilities in mind, let us examine the problem of developing a program to enable the computerto play tic-tac-toe with the user.
The game of tic-tac-toe at first appears to be a trivial game. New players quickly learn that a game played rationally by both sides must end in a draw. But being unbeatable does not mean you have mastered the game. The skilled player sets traps in the form of forks so that there are two ways to complete a row of three, only one of which can be blocked by the opponent. There are 15120 different sequences for the first five moves alone, counting rotations and reflections, but these may be reduced to a manageable number of possibilities. There are only three basic opening moves: center, side, and corner. The corner opening is strongest; only by taking the center can the second player avoid an immediate trap. With a side opening or with a center opening, the second player has four choices to avoid an immediate trap. For the side opening game, these safe choices are the three adjacent cells or the opposite side. For the center opening game, the safe choices are the four corners. [...] »
How to unwrap what was previously wrapped
[author : Ralph Stirling] #Electronic
A disassembler can save countless headaches
[author : Edward R Teja and Gary Gonnella] #Listing #Assembly #Programming
Extract : « Software development in machine language is a difficult task. A substantial part of the frustration can be traced to the difficulties of debugging a program when one must work from a printout that has no flow, no mnemonics, and bears little resemblance to any real world logic system. A disassembler can save the programmer countless headaches by correcting these deficiencies. This particular disassembler was constructed to aid in the development of software for a dedicated controller for an amateur radio repeater.
The basic requirements for our disassembler are that it use a small amount of memory (this version uses less than 750 bytes of memory, satisfying our definition of small), and that it provide a readable listing that includes mnemonics. The only restriction of this version is that it will print a maximum of only hexadecimal FF addresses (eg: hexadecimal 0400 to 04FF) without being restarted. [...] »
A personal routine helps increase accuracy
[author : Erich A Pfeiffer] #Algorithm #Listing #Assembly
Extract : « Resident assembler programs and interpreters for high level languages are available increasingly for microcomputer systems based on the more popular microprocessors. Nevertheless, many operators of small microcomputer systems are unable to use such programs because their systems are not large enough to support them. Unless they are lucky enough to have access to a timesharing service or to some larger computer which supports a cross assembler, their only way of developing a usable object program is to assemble it by hand.
While the mere idea of such an endeavor might horrify any programmer who is used to working with large machines, the hand assembly of shorter programs for 8 bit microprocessors actually is not very difficult. It has been my experience that the assembly of programs can be greatly simplified and the likelihood of errors can be reduced by using some simple aids in the assembly process. [...] »
#Association
#Book
Extract : « Practical Microcomputer Programming: The INTEL 8080 by W J Welter, A V Shatzel, and H Y Nice Northern Technology Books Evanston IL 1976 306 pages hardcover, 6 1/2 by 9 1/4 Inches $21.95 [...]
Structured Programming in APL by Dennis P Geller and Daniel P Freedman Winthrop Publishers Inc, 1976 Englewood Cliffs NJ $9. 95 [...]
The Cheap Video Cookbook by Don Lancaster Howard W Sams and Co Indianapolis IN, 1978 $5.95 [...]
Microcomputer-Based Design by John B Peatman McGraw-Hill, New York 540 pages, 6 1/2 by 9 1/2 inches $24.50 [...] »