Seven-segment display
A seven-segment display, or seven-segment indicator, is a form of electronic display device for displaying decimal numerals, an alternative to the more complex dot matrix displays. Seven-segment displays are used in digital clocks, electronic meters, basic calculators, other electronic devices that display numerical information; the seven elements of the display can be lit in different combinations to represent the Arabic numerals. The seven segments are arranged in an oblique arrangement, which aids readability. In most applications, the seven segments are of nearly uniform shape and size, though in the case of adding machines, the vertical segments are longer and more oddly shaped at the ends in an effort to further enhance readability; the numerals 6 and 9 may be represented by two different glyphs on seven-segment displays, with or without a'tail'. The numeral 7 has two versions, with or without segment F; the seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top and bottom.
Additionally, the seventh segment bisects the rectangle horizontally. There are fourteen-segment displays and sixteen-segment displays. Twenty-two segment displays capable of displaying the full ASCII character set were available in the early 1980s, but did not prove popular; the segments of a 7-segment display are referred to by the letters A to G, where the optional decimal point is used for the display of non-integer numbers. Seven-segment displays may use a liquid crystal display, a light-emitting diode for each segment, an electrochromic display, or other light-generating or controlling techniques such as cold cathode gas discharge, vacuum fluorescent, incandescent filaments, others. For gasoline price totems and other large signs, vane displays made up of electromagnetically flipped light-reflecting segments are still used. An alternative to the 7-segment display in the 1950s through the 1970s was the cold-cathode, neon-lamp-like nixie tube. Starting in 1970, RCA sold a display device known as the Numitron that used incandescent filaments arranged into a seven-segment display.
In a simple LED package all of the cathodes or all of the anodes of the segment LEDs are connected and brought out to a common pin. Hence a 7 segment plus decimal point package will only require nine pins, though commercial products contain more pins, and/or spaces where pins would go, in order to match standard IC sockets. Integrated displays exist, with single or multiple digits; some of these integrated displays incorporate their own internal decoder, though most do not: each individual LED is brought out to a connecting pin as described. Multiple-digit LED displays as used in pocket calculators and similar devices used multiplexed displays to reduce the number of I/O pins required to control the display. For example, all the anodes of the A segments of each digit position would be connected together and to a driver circuit pin, while the cathodes of all segments for each digit would be connected. To operate any particular segment of any digit, the controlling integrated circuit would turn on the cathode driver for the selected digit, the anode drivers for the desired segments.
In this manner an eight digit display with seven segments and a decimal point would require only 8 cathode drivers and 8 anode drivers, instead of sixty-four drivers and IC pins. In pocket calculators the digit drive lines would be used to scan the keyboard as well, providing further savings. Although to a naked eye all digits of an LED display appear lit, the implementation of a typical multiplexed display described above means that in reality only a single digit is lit at any given time. A single byte can encode the full state of a 7-segment-display; the most popular bit encodings are gfedcba and abcdefg, where each letter represents a particular segment in the display. In the gfedcba representation, a byte value of 0x06 would turn on segments'c' and'b', which would display a'1'. Seven-segment representation of figures can be found in patents as early as 1903, when Carl Kinsley invented a method of telegraphically transmitting letters and numbers and having them printed on tape in a segmented format.
In 1908, F. W. Wood invented an 8-segment display, which displayed the number 4 using a diagonal bar. In 1910, a seven-segment display illuminated by incandescent bulbs was used on a power-plant boiler room signal panel, they were used to show the dialed telephone number to operators during the transition from manual to automatic telephone dialing. They did not achieve widespread use until the advent of LEDs in the 1970s, they are sometimes used in posters or tags, where the user either applies color to pre-printed segments, or applies color through a seven-segment digit template, to compose figures such as product prices or telephone numbers. For many applications, dot-matrix LCDs have superseded LED displays, though in LCDs 7-segment displays are common. Unlike LEDs, the shapes of elements in an LCD panel are arbitrary since they are formed on the display by a kind of printing process. In contrast, the shapes of
TI-55
The TI-55 is a programmable calculator first manufactured by Texas Instruments in 1977. It had an LED display, weighed 6.4 ounces. It was programmable to hold up to 32 key-codes that would allow the user to repeat simple calculations with different values; the TI-55 II with LCD was introduced in 1981, like many other Texas Instruments calculators of this time, suffered from serious keyboard reliability problems. Several variants of the TI-55 II exist; the TI-55 III replaced the TI-55 II in the USA in 1986. It featured a redesigned keyboard mechanics, thereby eliminating the common "bouncing keys" fault of prior models. Several variants of the TI-55 III exist; the TI-56 was a European variant of the TI-55 III manufactured since 1986. It was offered free of charge in exchange of faulty Texas Instruments calculators of a similar class like the TI-54 in Europe in 1986
Zilog Z80
The Z80 CPU is an 8-bit based microprocessor. It was introduced by Zilog in 1976 as the startup company's first product; the Z80 was conceived by Federico Faggin in late 1974 and developed by him and his then-11 employees at Zilog from early 1975 until March 1976, when the first working samples were delivered. With the revenue from the Z80, the company built its own chip factories and grew to over a thousand employees over the following two years; the Zilog Z80 was a software-compatible extension and enhancement of the Intel 8080 and, like it, was aimed at embedded systems. According to the designers, the primary targets for the Z80 CPU were products like intelligent terminals, high end printers and advanced cash registers as well as telecom equipment, industrial robots and other kinds of automation equipment; the Z80 was introduced on the market in July 1976 and came to be used in general desktop computers using CP/M and other operating systems as well as in the home computers of the 1980s.
It was common in military applications, musical equipment, such as synthesizers, in the computerized coin operated video games of the late 1970s and early 1980, the arcade machines or video game arcade cabinets. The Z80 was one of the most used CPUs in the home computer market from the late 1970s to the mid-1980s. Zilog licensed the Z80 to the US-based Synertek and Mostek, which had helped them with initial production, as well as to a European second source manufacturer, SGS; the design was copied by several Japanese, East European and Soviet manufacturers. This won the Z80 acceptance in the world market since large companies like NEC, Toshiba and Hitachi started to manufacture the device. In recent decades Zilog has refocused on the ever-growing market for embedded systems and the most recent Z80-compatible microcontroller family, the pipelined 24-bit eZ80 with a linear 16 MB address range, has been introduced alongside the simpler Z180 and Z80 products; the Z80 came about when physicist Federico Faggin left Intel at the end of 1974 to found Zilog with Ralph Ungermann.
At Fairchild Semiconductor, at Intel, Faggin had been working on fundamental transistor and semiconductor manufacturing technology. He developed the basic design methodology used for memories and microprocessors at Intel and led the work on the Intel 4004, the 8080 and several other ICs. Masatoshi Shima, the principal logic and transistor level-designer of the 4004 and the 8080 under Faggin's supervision, joined the Zilog team. By March 1976, Zilog had developed the Z80 as well as an accompanying assembler based development system for its customers, by July 1976, this was formally launched onto the market. Early Z80s were manufactured by Synertek and Mostek, before Zilog had its own manufacturing factory ready, in late 1976; these companies were chosen because they could do the ion implantation needed to create the depletion-mode MOSFETs that the Z80 design used as load transistors in order to cope with a single 5 Volt power supply. Faggin designed the instruction set to be binary compatible with the Intel 8080 so that most 8080 code, notably the CP/M operating system and Intel's PL/M compiler for 8080, would run unmodified on the new Z80 CPU.
Masatoshi Shima designed most of the microarchitecture as well as the gate and transistor levels of the Z80 CPU, assisted by a small number of engineers and layout people. CEO Federico Faggin was heavily involved in the chip layout work, together with two dedicated layout people. Faggin worked 80 hours a week in order to meet the tight schedule given by the financial investors, according to himself; the Z80 offered many improvements over the 8080: An enhanced instruction set including single-bit addressing, shifts/rotates on memory and registers other than the accumulator, rotate instructions for BCD number strings in memory, program looping, program counter relative jumps, block copy, block input/output, byte search instructions. The Z80 had better support for signed 8 - and 16-bit arithmetics. New IX and IY index registers with instructions for direct base+offset addressing A better interrupt system A more automatic and general vectorized interrupt system, mode 2 intended for Zilog's line of counter/timers, DMA and communications controllers, as well as a fixed vector interrupt system, mode 1, for simple systems with minimal hardware.
A non maskable interrupt which can be used to respond to power down situations or other high priority events. Two separate register files, which could be switched, to speed up response to interrupts such as fast asynchronous event handlers or a multitasking dispatcher. Although they were not intended as extra registers for general code, they were used that way in some applications. Less hardware required for power supply, clock generation and interface to memory and I/O Single 5-volt power supply. Single-phase 5 V clock. A built-in DRAM refresh mechanism. Non-multiplexed buses. A special reset function which clears only the program counter so that a single Z80 CPU could be used in a
TI-59 / TI-58
The TI-59 is an early programmable calculator, manufactured by Texas Instruments from 1977. It is the successor to the TI SR-52, quadrupling the number of "program steps" of storage, adding "ROM Program Modules". Just like the SR-52, it has a magnetic card reader for external storage. One quarter of the memory is stored on each side of one card; the TI-58, TI-58C, are cut down versions of the TI-59, lacking the magnetic card reader and having half the memory, but otherwise identical. Although the TI-58C uses a different chip than the TI-58, the technical data remain identical; the "C" in a TI model name indicates that the calculator has a constant memory allowing retention of programs and data when turned off. These calculators use a parenthesized infix calculation system called "Algebraic Operating System", compared to the postfix RPN system used by other scientific calculators, the operator enters calculations just as they are written on paper, using up to nine levels of parenthesis; the calculator can be powered from an external adapter or from internal NiCd rechargeable battery pack.
The red LED display shows 10 decimal digits of precision. Programming simple problems with the TI-59 or TI-58 is a straightforward process. In programming mode, the TI-59 records key presses. Alphabetical keys provide easy access to up to ten entry points, it is possible to activate any of the programs in the pre-programmed memory module, run one like any user-written program. Programs written by the user can use programs in the module as subroutines; the module's programs run directly from ROM, so they leave the calculator's memory free for the user. However, exploiting the computer-like capabilities of the TI-59 is a different matter. Although the TI-59 is Turing-complete, supporting straight-line programming, conditions and indirect access to memory registers, although it supports limited alphanumeric output on the printer only, writing sophisticated routines is a matter of planning machine language and using a coding pad. A large degree of sharing occurred in the TI-58 community. At least one game, Darth Vader's Force Battle, appeared as a type-in program.
Here is a sample program that computes the factorial of an integer number from 2 to 69. For 5!, you'll type 5 A and get the result, 120. Unlike the SR-52, the TI-59 or TI-58 don't have the factorial function built-in, but do support it through the software module, delivered with the calculator. Op-code Comment LBL A You'll call the program with the A key STO 01 stores the value in register 1 1 starts with 1 LBL B label for the loop * multiply RCL 01 by n DSZ 1 B decrements n and back to B until n=0 = end of loop, the machine has calculated 1*n**...2*1=n! INV SBR end of procedure Here is the same program written for TI Compiler: #reg 01 counter #label A factorial LBL factorial STO counter 1 FOR counter * @counter LOOP = RTN #end In comparison to its contemporary main competitor, Hewlett-Packard HP-67, the TI-59 has about twice the memory; the partition between program steps and memories is adjustable in increments of 80 program steps/10 memories, as many as 960 program steps or as many as 100 memories can be configured.
The TI-59 was the first programmable pocket calculator where the manufacturer provided a system for sharing memory between data registers and program storage. The memory is only about twice as large as in the SR-52, but more flexible, thus the possible number of program steps was four times as high. Contents of this memory are lost; the TI-58 supports up to 480 program steps or 60 memories. It competed with the HP-34C; the TI-58 and TI-59 calculators have variable length instructions. Some keypresses are merged into one programming step, so that instructions from one to eleven keypresses are stored in one to six programming steps; the HP-67 always stores one instruction in one programming step, efficient for some used instructions but limits the number of possible instructions. The TI-59 can store programs and data on small magnetic cards when the calculator is turned off and reloaded when needed. Click below for a video of the card reader in action; the video shows the dual use of the magnetic card as a program documentation menu.
Notes can be handwritten by the programmer on the top side of the magnetic card. Once read by the cardreader, the card can be stored, as shown, in a slot between the top of the keyboard and the display, thus providing a notation indicating both the name of the program loaded and the purpose of each of the five label buttons A-E and their secondary functions A'-E' within the loaded program; the TI-58 does not have a magnetic card reader. The TI-59 and TI-58 were the first hand-held calculators to utilize removable ROM program modules; the Master Library Module ROM was included with the TI-59 and TI-58, contains several useful pre-programmed routines and a game. Additional modules - for such applications as real estate, statistics and aviation - were sold separately; the programs in the modules used the user-defined keys heavily. To make the programs easier to use, plastic cards with the same size as the magnetic cards, but just printed to label the user-defined keys, can be inserted
TI SR-50
The SR-50 was Texas Instruments' first scientific pocket calculator with trigonometric and logarithm functions. It enhanced their earlier SR-10 and SR-11 calculators, introduced in 1973, which had featured scientific notation, square root, reciprocals, but had no trig or log functions, lacked other features; the SR-50 was introduced in 1974 and sold for US$170. It competed with the Hewlett-Packard HP-35; the SR-50 measured 5-3/4 inches long by 3-1/8 inches wide by 1-3/16 inches high and was powered by a rechargeable NiCad battery pack, built from three soldered AA cells. It had 40 keys, flat sliding switches for degrees/radians and on/off. "SR" stood for "slide rule." The SR-50 had a red LED display with a signed ten-digit mantissa plus a signed two-digit exponent for floating point numbers. Internally, calculations were performed with a 13-digit mantissa, providing much greater calculation accuracy than the 10-digit precision of most scientific calculators of the time. After the leading sign, digits consisted of a seven-segment display plus decimal point.
A blinking display indicated an error, such as a calculation error or an overflow or underflow condition. Like most scientific calculators, the SR-50 used ordinary infix notation, as opposed to the postfix Reverse Polish Notation employed by its competitor, the Hewlett Packard HP-35; the SR-50 followed the standard order of operations by performing unary operations and multiplication, division and power operations before addition and subtraction operations. As an example, the keypresses to calculate "3 x log + 5" was entered as written, namely "3 x 4 log + 5 ="; this is because the calculator would execute the log function before performing the multiplication operation, complete the multiplication operation before executing the addition operation. It did so by having unary operations operate on the X register and subtraction operate on the X and Z registers, multiplication, division and root functions operate on the X and Y registers in its operational stack. An unusual feature of the SR-50 was that its included functions like factorial and hyperbolic trig functions, which were found on few calculators at the time.
The user invoked the hyperbolic functions by entering the function argument and pressing the "hyp" key, followed by the "sin", "cos", or "tan" function key. The inverse hyperbolic functions were accessed by first pressing the "arc" and "hyp" keys and pressing the "sin", "cos", or "tan" key. Hyperbolic trig arguments were always assumed to be in radians regardless of the setting of the degree/radian mode switch. In addition to its three-register operational stack, consisting of X, Y, Z registers, the SR-50 included one memory register to which the value in the X register could be directly added using the "summation" key; the SR-50 had fast trig functions and was a popular calculator to use in contests involving pocket calculators. ALU: TMC0501 SCOM: TMC0521 Display driver: 2 × 27882 Power: NiCd battery pack BP1, charger AC9200 or AC9900 The SR-50 was followed by the more advanced model SR-51; the SR-51 added a 2nd function for most buttons. Most notable among the added functions were the ability to enter x:y pairs and do linear regression analysis on them.
The and lighter versions SR-50A and SR-51II and SR-51III were based on smaller ICs and battery packs and reached broadest distribution. A further update resulted in the programmable model SR-52 in late 1975, it was thicker and longer and could perform 224 program steps recorded on magnetic cards, similar to its competitor HP-65. The card was pulled through the reader by an electric motor; the matte white upper face of the cards could be marked with pen or pencil to indicate the program and the functions assigned to the calculator's programmable keys. The card could be stored in a slot above the programmable keys with its markings visible. In 1976 Texas Instruments released the TI-30 budget calculator at one-third the price of the SR-50, so sales of the SR-50 dropped
Microcomputer
A microcomputer is a small inexpensive computer with a microprocessor as its central processing unit. It includes a microprocessor and minimal input/output circuitry mounted on a single printed circuit board. Microcomputers became popular in the 1970s and 1980s with the advent of powerful microprocessors; the predecessors to these computers and minicomputers, were comparatively much larger and more expensive. Many microcomputers are personal computers; the abbreviation micro was common during the 1970s and 1980s, but has now fallen out of common usage. The term microcomputer came into popular use after the introduction of the minicomputer, although Isaac Asimov used the term in his short story "The Dying Night" as early as 1956. Most notably, the microcomputer replaced the many separate components that made up the minicomputer's CPU with one integrated microprocessor chip; the French developers of the Micral N filed their patents with the term "Micro-ordinateur", a literal equivalent of "Microcomputer", to designate a solid state machine designed with a microprocessor.
In the USA, the earliest models such as the Altair 8800 were sold as kits to be assembled by the user, came with as little as 256 bytes of RAM, no input/output devices other than indicator lights and switches, useful as a proof of concept to demonstrate what such a simple device could do. However, as microprocessors and semiconductor memory became less expensive, microcomputers in turn grew cheaper and easier to use: Increasingly inexpensive logic chips such as the 7400 series allowed cheap dedicated circuitry for improved user interfaces such as keyboard input, instead of a row of switches to toggle bits one at a time. Use of audio cassettes for inexpensive data storage replaced manual re-entry of a program every time the device was powered on. Large cheap arrays of silicon logic gates in the form of read-only memory and EPROMs allowed utility programs and self-booting kernels to be stored within microcomputers; these stored programs could automatically load further more complex software from external storage devices without user intervention, to form an inexpensive turnkey system that does not require a computer expert to understand or to use the device.
Random access memory became cheap enough to afford dedicating 1-2 kilobytes of memory to a video display controller frame buffer, for a 40x25 or 80x25 text display or blocky color graphics on a common household television. This replaced the slow and expensive teletypewriter, common as an interface to minicomputers and mainframes. All these improvements in cost and usability resulted in an explosion in their popularity during the late 1970s and early 1980s. A large number of computer makers packaged microcomputers for use in small business applications. By 1979, many companies such as Cromemco, Processor Technology, IMSAI, North Star Computers, Southwest Technical Products Corporation, Ohio Scientific, Altos Computer Systems, Morrow Designs and others produced systems designed either for a resourceful end user or consulting firm to deliver business systems such as accounting, database management, word processing to small businesses; this allowed businesses unable to afford leasing of a minicomputer or time-sharing service the opportunity to automate business functions, without hiring a full-time staff to operate the computers.
A representative system of this era would have used an S100 bus, an 8-bit processor such as an Intel 8080 or Zilog Z80, either CP/M or MP/M operating system. The increasing availability and power of desktop computers for personal use attracted the attention of more software developers. In time, as the industry matured, the market for personal computers standardized around IBM PC compatibles running DOS, Windows. Modern desktop computers, video game consoles, tablet PCs, many types of handheld devices, including mobile phones, pocket calculators, industrial embedded systems, may all be considered examples of microcomputers according to the definition given above. Everyday use of the expression "microcomputer" has declined from the mid-1980s and has declined in commonplace usage since 2000; the term is most associated with the first wave of all-in-one 8-bit home computers and small business microcomputers. Although, or because, an diverse range of modern microprocessor-based devices fit the definition of "microcomputer", they are no longer referred to as such in everyday speech.
In common usage, "microcomputer" has been supplanted by the term "personal computer" or "PC", which specifies a computer, designed to be used by one individual at a time, a term first coined in 1959. IBM first promoted the term "personal computer" to differentiate themselves from other microcomputers called "home computers", IBM's own mainframes and minicomputers. However, following its release, the IBM PC itself was imitated, as well as the term; the component parts were available to producers and the BIOS was reverse engineered through cleanroom design techniques. IBM PC compatible "clones" became commonplace, the terms "personal computer", "PC", stuck with the general public specifically for a DOS or Windows-compatible computer. Monitors and other devices for inpu
TI-57
The TI-57 was a programmable calculator made by Texas Instruments between 1977 and 1982. There were three machines by this name made by TI, the first was the TI-57 with LED display released in September 1977 along the more powerful TI-58 and TI-59, it had 8 memory registers. Two versions named TI-57 LCD and TI-57 LCD-II have a LCD display, but were less powerful and had much less memory: 48 bytes to be allocated between program'steps' and storage registers; the TI-57 lacked non-volatile memory, so any programs entered were lost when the calculator was switched off or the battery ran out. The LED display version of the TI-57 had a rechargeable Nickel-Cadmium battery pack BP7 which contains two AA size batteries and electronics to raise the voltage to the 9V required by the calculator. A popular modification is to power it from a 9V battery and use the battery cover of a LED TI-30 or a part of the dismantled battery pack; this modification provides a better battery life than the original battery pack.
Included, with at least the original version was a book entitled "Making Tracks Into Programming". It was self described as "A step-by-step learning guide to the power and fun of using your TI Programmable 57". Radio Shack marketed this calculator, rebranded as the EC-4000; the programming capabilities of the TI-57 were similar to a primitive macro assembler. Any keystroke could be stored, along with some simple program flow control commands and conditional tests; these included: GTO: Causes program pointer to jump to a Label or to a specific program step. SBR: Causes a program to jump to a Label, on encountering an Inv SBR command, continue executing at the instruction following the original SBR. DSZ: Decrements storage register zero, skips the next instruction if the result is zero. There was an inverse form and Skip if Not Zero. Tests for equality/inequality could be performed against a value on the display and a dedicated test register, t; the result of the test would cause the next instruction to be conditionally skipped.
Programs could be edited by deleting, or overwriting a program step. A NOP function was provided to allow a program step to be ignored. Due to the hard limit of 50 program steps, use of NOP was infrequent; the TI-57 used the "one step, one instruction" principle, regardless of whether one instruction required one or up to four keypresses. The following program generates pseudo-random numbers within the range of 1 to 6. TI-57 on MyCalcDB TI-57 on The Datamath Calculator Museum
