TRS-80
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- For the Chicago-based electronica group, see TRS-80 (group).
TRS-80 was Tandy Corporation's desktop microcomputer model line, and sold through Tandy's RadioShack stores, in the late-1970s and 1980s. Hobbyists, home users, and small-businesses were the intended consumers.
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[edit] Early Z80-based home systems
[edit] History
Announced at a press conference on August 3, 1977, the Tandy TRS-80 Model I was Tandy's entry into the home computer market, meant to compete head on against the Commodore PET 2001 and the Apple II. At $599 for a complete package including cassette storage, the computer was the most expensive single product Tandy's Radio Shack chain of electronics stores had ever offered. Company management was unsure of the computer's market appeal, and intentionally kept the initial production run to 3,000 units so that, if the computer failed to sell, it could at least be used for accounting purposes within the chain's 3,000 stores.
Tandy ended up selling 10,000 the first month and 55,000 its first year. Before its January 1981 discontinuation, Tandy sold more than 250,000 Model I's.
[edit] Hardware
The Model I combined the motherboard and keyboard into one unit, in what was to be a common case-design trend throughout the 8 and 16 bit microcomputer eras, although it had a separate power supply unit. It used a Zilog Z80 processor clocked at 1.77 MHz. The basic model originally shipped with 4 KiB of RAM, and later 16 KiB.
[edit] Keyboard
The transfer of information about what keys were being pressed was unusual, in that instead of transferring data via an I/O device or chip, the hardware mapped the keyboard to pre-defined locations in memory, i.e., there was no 'real' memory at this location, but performing a read from the keyboard area of the memory map would return the state of a particular set of keys.
A version of the computer was produced which replaced the nameplate with a numeric keypad.
Many users complained about the TRS-80 keyboards which were mechanical switches and suffered from "Keyboard Bounce" resulting in multiple letters being typed accidentally. A Keyboard De-Bounce tape was distributed to compensate, which both ignored key contact closures if they were detected within a short time of a contact opening, and slowed down polling of the keyboard. Eventually, this was added to a later ROM revision. The keyboard was also changed to be less vulnerable to bounce.
[edit] Video
It was accompanied by a white on black display, which was a modified RCA XL-100 Black and White television. The actual color of the system was light bluish (the standard "P4" phosphor used in black-and white televisions), and green and amber filters or replacement tubes, to make the display easier on the eyes, were a common after market item. Because of bandwidth problems in the interface card that replaced the TV's tuner, the display would lose horizontal sync if large areas of white were displayed; a simple hardware fix (involving less than half an hour's work) could be applied to correct that.
The video hardware could only display text at 64 or 32 characters wide by 16 lines resolution in upper case. This was because the video memory system used a single kilobyte of video memory. Seven of these bits were used to display ASCII characters with the eighth bit used to differentiate between text and "semigraphics" characters. Although the original TRS-80 Model I could differentate between upper and lower characters in memory, only upper characters were displayed, and third party modifications to allow the Model I to display lower case characters were a popular add on.
Primitive graphics ("text semigraphics," rather than a true bitmap) could be displayed because the upper 64 characters of the 128 character set displayed as a grid of 2×3 blocks (very similar to Teletext). BASIC programs could write directly to the resulting 128×48 grid.
Any access to the screen memory, writing to it using the BASIC statement PRINT or accessing the screen memory directly, caused "flicker" on the screen. The bus arbitration logic would block video display while access was given to the CPU (causing a short black line). Normal BASIC programs would not be much affected by this, but fast programs made in assembly might be badly affected by this effect if the programmer didn't take it into consideration. This was not as bad as a Timex ZX81, where the entire screen flickered, and many software authors were able to minimize this effect. Not withstanding this primitive display hardware many arcade-style games were available for the Tandy TRS-80.
[edit] Peripherals
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User data was originally stored on cassette tape. A standard monaural audio cassette deck (CTR-41) was included with the machine. The cassette tape interface was extremely sensitive to audio volume changes, and the machine only gave the very crudest indication as to whether the correct volume was set, via a blinking character on screen when data was actually being loaded - to find the correct volume, one would sometimes have to attempt to load a program once adjusting volume until the machine picked up the data, then reset the machine, rewind the tape and attempt the load again. Users quickly learned to save a file three or more times in hopes that one copy would prove to be readable. Automatic gain control or indicator circuits could be constructed to compensate for this, (fortunately the owner's manual provided complete circuit diagrams for the whole machine, including the peripheral interfaces, with notes on operation) and there was also an alternative tape interface that one could build in order to receive transmissions from the BBC's "Chip Shop" programme in the UK, an experiment in transmitting free software for several different BASIC home microcomputers, in a common tape format, over the radio. A special program (loaded using the conventional tape interface) was needed to access the custom interface over the expansion port and then load the recorded software. Tandy eventually replaced the CTR-41 unit with the CTR-80 which had built in AGC circuitry (and no volume control). This helped the situation but tape operation was still unreliable.
TRS-80's with Level I Basic read and wrote tapes at 250 baud, however "baud" was a misnomer in this application. The data rate was 25 bytes per second. Level II Basic doubled this to 500 "baud" or 50 bytes per second.
To upgrade to a floppy disk based system the owner had to buy the "Expansion Interface" (or "E/I") that added a "single density" floppy disk interface. This was based on a Western Digital 1771 single density floppy disk controller chip, but it lacked a separate external "data separator", and was thus very unreliable. There was also the ability to expand to up to a total of 48k of RAM, a second cassette tape port to use two tapes simultaneously, a serial interface (option) and a Centronics printer interface. The Expansion Interface was the most troublesome part of the system, having gone through several modifications (a pre-production version is said to have looked completely different, and to have had a card cage) before on-board buffering of the bus connector lines cured its chronic problems with random lockups and crashes. Its edge card connectors tended to corrode due to the use of two different metals in contact, and would periodically have to be cleaned with a pencil eraser. The E/I required a second power supply unit identical to that of the TRS-80 itself, but was designed with a recess in its casing capable of holding both PSU units and removing some of the clutter around the system. The E/I-TRS-80 cable was also only a couple of inches in length, meaning the user had no choice but to use the official layout of placing the E/I directly behind the computer and placing the monitor on top of the E/I - this caused problems if one owned a monitor whose case did not fit the E/I mounting holes, as mentioned above. The short length of interconnect cable also meant that the unit could easily be disconnected accidentally if the main unit was moved.
One unusual peripheral offered was a "screen printer": an electrostatic rotary printer that scanned the video memory through the same bus connector used for the E/I, and printed an image of the screen onto aluminum-coated paper in about a second. Unfortunately, it was incompatible with both the final, buffered version of the E/I, and with the "heartbeat" interrupt used for the real-time clock under Disk BASIC. This could be overcome by using special cabling, and by doing a "dummy" write to the cassette port while triggering the printer.
For Printing, there were offered another two printers: one for 57mm metal coated paper, selling at approx. 600 Deutschmark in Germany, and one Centronics (the name does not only stand for its interface, but for the manufacturer, Centronics Company) for normal paper, costing at first 3000 Deutschmark, later sold at approx. 1500 Deutschmark in some stores. It had 7 pins so letters like "g" did not reach under the baseline, but were elevated within the normal line.
At first, the Expansion Interface was needed for the printers, which was quite expensive. Soon, Tandy Corp. sold a parallel Interface Cable at only approx. 300 Deutschmark in Germany.
A Data Separator and/or a Double Density disk controller (based on the WD 1791 chip) were made available by Percom (a Texas Peripheral Vendor), LNW, Tandy and others. The Percom Doubler added the ability to boot and use Double Density Floppies (they provided their own modified TRSDOS called DoubleDOS), and included the Data Separator. The LNDoubler added the ability to read and write from 8" Diskette Drives for over 1.2mb of Storage.
All TRS-80 disk formats were soft-sectored with index-sync (as opposed to the Apple II formats, which were soft-sectored without index sync, with many Apple drives lacking even an index hole detector), and except for some very early Shugart drives (recognizable by their spiral-cam head positioner), all TRS-80 floppy drives were 40-track double-density models. The combination of 40 tracks, double-density, and index-sync gave a maximum capacity of 180 kilobytes per single-sided floppy disk, considerably higher than most other systems of the era. On the other hand, the use of index-sync meant that in order to turn a floppy disk into a "flippy," it was necessary not only to cut a second write-enable notch, but also to punch a second index hole window in the jacket (at great risk to the disk inside). Or one could purchase factory-made "flippies," or use the back side for Apple Computer systems (as some software publishers of the era did).
[Edit: the drives sold by Radio Shack were 35-track models with a 160K capacity.]
[edit] BASIC
There were two versions of the BASIC programming language produced for the Model I. Level I BASIC fit in 4 KiB of ROM, and Level II BASIC fit into 12 KiB of ROM. Level I was single precision only and had a smaller set of commands. Level II introduced double precision floating point support and had a much wider set of commands. Level II was further enhanced when a disk system was added, and the Disk Based BASIC was loaded.
Level I Basic was Li-Chen Wang's free Tiny Basic, hacked by Radio Shack to add functionality. It achieved a measure of noteworthiness due in large part to its outstanding manual, written by David Lien, which presented lessons on programming with text and colorful graphics, making the subjects very easy to understand. The basic had only two stringvariables (a$ and b$), 25-23 variables and just the possibility of one array. Basic code for functions like sin(), cos() and tan() was not included in ROM but printed at the end of the book. The error messages were: "WHAT?", "HOW?", and "SORRY".
Level II BASIC was licensed from Microsoft. It was a cut down version of the 16 KiB Extended BASIC, since the Model I had 12 KiB of ROM space. The accompanying manual was not nearly as colorful and suited for beginning programmers as the Level I Basic manual. Users had to take their TRS-80 computers to the Radio Shack dealers to have the machines upgraded from Level I to Level II BASIC.
See "TRS-80 architect.htm" (TRS-80 architect reminisces about design project) for a complete discussion.
The Disk Based BASIC added the ability to perform disk I/O, and in some cases (NewDos/80, MultiDOS, DosPlus, LDOS) added powerful sorting, searching, full screen editing, and other features. Level II BASIC recognized some of these commands and issued a "?L3 ERROR", suggesting that a behind-the-scenes change of direction intervened between the recording of the Level II ROMs and the introduction of Disk BASIC, which Radio Shack didn't call Level III.
Microsoft also marketed a tape-cassette based enhanced BASIC called Level III BASIC. This added most of the functions in the full 16 KiB version of Basic.
The first models of the Model I also had problems reading from the cassette drives. Tandy eventually offered a small board which was installed in a service center to correct earlier models. The ROMs in later models were modified to correct this.
TRS-DOS--Radio Shack's operating system for its TRS-80 computers--was so crummy that most discerning TRS-80 owners spurned it in favor of NewDOS, a third-party rival sold by a company called Apparat. (Apparat Personal Computers, Denver CO went out of business in 1987) (Eventually, it was one of multiple TRS-80 alternatives--others included LDOS, DOSPLUS, and VTOS.) Radio Shack probably didn't consider it an upgrade to TRS-DOS, but the owners sure did.
[edit] Software applications
Quite a few popular software applications were available for the TRS-80. Many leading developers, and independent software companies such as Big Five, ported over popular arcade hits like Namco's Pac Man and Galaxian, Atari's Centipede Sega's Zaxxon and Stern electronics Berzerk (with digitized speech). Or ported games from other home computers of the area, such as such as the original Zork adventure game. But there were also many games unique to the TRS-80, often shooters like Cosmic Fighter and Defence Command but also strange experimental programs such as dancing demon, which was not strictly spoken a game but did have a big entertainment value.
The TRS-80 also had a full suite of office applications, including the VisiCalc and As-Easy-As spreadsheets and the Lazy Writer and Electric Pencil word processors.
[edit] Clones
Many clones of the TRS-80 Model I came on the market: the LOBO Max-80 (Lobo also produced their own version of the Expansion Interface), the LNW-80 Models I/II and Team Computers (LNW also produced an alternate version of the Expansion Interface), and the Dutch Aster CT-80.
EACA in Hong Kong made a Model I clone that was marketed around the world under different names with modifications. In Australia and New Zealand it was the Dick Smith System-80, in North America it was PMC-80 and PMC-81, in Hungary the HT-1080Z, in South Africa the TRZ-80, and in Western Europe it was Video Genie. The expansion bus was different and EACA also made its own Expansion Interface to fit it. There were several versions and it was later split into a 'home' and a 'business' version, Genie I and II, and System-80 Mark I and II, where the II would have a numeric keypad instead of the inbuilt cassette player. EACA's Colour Genie was also based on TRS-80 Model I but with improved graphics and other changes it was not very compatible.
In Brazil there were several manufacturers of different Model I/III/IV clones. Digitus made the DGT-100 and DGT-1000, Prologica made the highly-successful CP300 and CP500 series, Sysdata Eletrônica Ltda. made the Sysdata Jr. Dismac made the D8000/D8001/D8002 series. Prologica also made the CP400 / CP 400II which were copies of the TRS80-Color, with the external case being almost a copy of the Timex 2068.
[edit] Model III
As a follow on to the Model I, in July 1980 Tandy released the Model III, a more integrated and much improved Model I. The improvements of the Model III included built-in lower case, a better keyboard, and a faster (2.03 MHz) Z-80 processor. With the introduction of the Model III, Model I production was eventually discontinued as the Model I's did not comply with new FCC regulations regarding radio interference. In fact, the Model I's radiated so much RFI (Radio Frequency Interference) that many game companies made their games so you could put an AM radio next to the computer and use the interference to get sounds. The TRS-80 Model III also came with the option of integrated disk drives.
[edit] Model 4
The successor to the Model III was the Model 4 (April 1983, with "4" written as an Arabic numeral), which included the capability to run CP/M. (This had previously only been possible via a hardware modification that remapped the BASIC ROMs away from memory address zero.) Prior to the Model 4, CP/M support was only possible with a third-party add-on, sold as the Omikron Mapper board. The Model 4 also had the ability to display high-resolution graphics with an optional board. The Model 4 also came in a "luggable" version known as the Model 4P (1984) which was portable. It was a self-contained unit that looked like a small sewing machine.
[edit] Business systems
[edit] Model II
In October 1979, Tandy began shipping the Model II, which was targeted to the small-business market. It was not an upgrade of the Model I, but an entirely different system, built using the faster Zilog Z80A chip running at 4 MHz, with the computer, 8" floppy disk drive, and monochrome 80x24 monitor built into a single cabinet, DMA and vectored interrupts that the Model I lacked, and a detached keyboard. It was available with 32 KiB or 64 KiB of RAM; two RS-232 serial ports and a Centronics printer port were standard. Unlike the Model I, the video and keyboard were not memory-mapped, leaving the entire memory space available for programs. Hard disk drives and additional floppy drives were available as options. The Model II ran TRSDOS-II and BASIC. TRSDOS-II was not very compatible with TRSDOS for the Model I, thus the Model II never had the same breadth of available software as the Model I. This was somewhat mitigated by the availability of the CP/M operating system from third parties such as Pickles & Trout.
Tandy offered a desk custom-designed for the Model II for US$370. It could hold an additional three 8" disk drives or up to four 8.4MB hard drives.
Tandy eventually offered a 16 bit upgrade to the Model II, the Model 16. The Model II was later replaced by a cost-reduced Model 12, which added half-height 8" floppy drives, a green phosphor screen, and a white case, but dropped the expansion card cage (though one was available as an option).
[edit] Model 16, Model 16B, and Tandy 6000
Tandy later released the TRS-80 model 16, which was a follow on to the Model II; an upgrade was available to Model II owners. The Model 16 added a 6 MHz, 16 bit Motorola 68000 processor, keeping the original Z-80 as an I/O processor. It could run either TRSDOS-16 or Xenix, Microsoft's version of UNIX. Of the two operating systems, Xenix was far more popular. TRSDOS-16 was essentially a 68000 port of Model II TRSDOS, with no additional features and little compatible software.
Xenix, on the other hand, offered the full power of UNIX System III including multi-user support. The Model 16 family with Xenix became a popular system for small business, with a relatively large library of business and office automation software for its day. Tandy offered multi-user word processing (Scripsit 16), spreadsheet (Multiplan), and a 3GL "database" (Profile 16, later upgraded to filePro 16+), as well as an accounting suite with optional COBOL source for customization. RM-COBOL, Basic, and C were available for programming, with Unify and Informix offered as relational databases.
The Model 16 evolved into the Model 16B, and then the Model 6000, gaining an internal hard drive along the way and switching to an 8 MHz 68000 and half-height, 8-inch floppy drives (double-sided, double density, 1.2 MB). Tandy offered 8.4MB, 15 MB, 35 MB, and 70 MB hard drives, up to 768 KiB of RAM, and up to eight RS-232 serial ports supporting multi-user terminals. Additional memory and serial port expansion options were available from aftermarket companies.
Because the business systems were designed for work and not for home use, there is a lot less affection and nostalgia directed at them than at the Z-80 and Color Computer (Coco) systems.
[edit] Other systems
[edit] TRS-80 Color Computers
Tandy also produced the TRS-80 Color Computer (Coco) using a Motorola 6809 processor. This machine was clearly aimed at the home market, where the Model 2 and above were sold as business machines. It competed directly with the Commodore 64. OS-9, a multitasking, multi-user operating system was supplied for this machine.
[edit] TRS-80 Model 100 line
In addition to the above, Tandy produced the TRS-80 Model 100 series of "laptop" computers. This series comprised the TRS-80 Model 100, 102 and 200. The Model 100 was designed by the Japanese company Kyocera with software written by Microsoft. It is reported that the Model 100 featured the last code that Bill Gates ever wrote.
The Model 100 had an internal 300 baud modem, built-in BASIC, and a limited text editor. It was possible to use the Model 100 on essentially any phone in the world with the use of an optional acoustic coupler that fit over a standard telephone handset. The combination of the acoustic coupler, the machine's outstanding battery life (it could be used for days on a set of 4 AA batteries), and its simple text editor made the Model 100/102 popular with journalists in the early 1980s. The Model 100 line also had an optional serial/RS-232 floppy drive and a Cassette interface.
[edit] TRS-80 MC-10
This short-lived and little-known Tandy computer was similar in appearance to the Sinclair ZX81.
It was a small system based on the Motorola 6803 processor and featured 4k of RAM. A 16k RAM expansion pack that connected on the back of the unit was offered as an option as was a thermal paper printer.
Programs loaded using a cassette which worked much better than those for the Sinclair. A magazine published offered programs for both the COCO and MC-10 but very few programs were available for purchase. Programs for the MC-10 were not compatible with the COCO.
[edit] TRS-80 Pocket Computers
TRS-80 was also used for a line of Pocket Computers which were manufactured by Sharp or Casio, depending on the model.
[edit] TRS-80 PC-Compatible Computers
In the early-1980s, Tandy began producing a line of computers that were more or less PC compatible. Two of these systems were referred to as TRS-80 Model 2000 and Tandy 1000. As margins decreased in PC clones, Tandy was unable to compete and stopped marketing their own systems.
Originally, Tandy offered computers manufactured by Tandon Corporation, and then started producing their own line of systems.
The TRS-80 Model 2000 system was similar to the Texas Instruments Professional Computer in that it offered better graphics, a faster processor (80186) and higher capacity disk drives (80 track double sided 800k 5.25 drives). The industry was moving away from MS-DOS compatible computers (like the Sanyo MBC-550 and the TIPC) and towards fully compatible clones (like the Compaq, Eagle, Columbia MPC and others).
The later Tandy 1000 systems and follow-ons were also marketed by DEC, as Tandy and DEC had a joint manufacturing agreement.
[edit] Emulators
- Windows: HT1080Z EACA Emulator for Windows XP
- Windows: trs32 Model 1/3/4 Emulator for Win XP (shareware)
- Windows: Windows (shareware) Several TRS-80 Emulators; emulated in 80486+ Assembly
- Linux/Unix: xtrs (open-source)
- Java: Java applet
- Mac OS X: M.E.S.S. Emulator includes TRS-80 emulator
- Mac Classic: TRS-80 Emulator for Mac OS (no sound support) for Mac OS 7.5.5 or higher
[edit] See also
- List of TRS-80 games
- List of TRS-80 software
- Scripsit, the Tandy-branded word processor software
- 80 Micro, magazine devoted to the TRS-80
- Softside, magazine with BASIC programs for the TRS-80 and other microcomputers of the same era
[edit] External links
- Ira Goldklang's TRS-80 Revived Pages
- The History of the TRS-80
- Radio Shack Model I and II catalog RSC-3
- Jeff Hellige's TRS-80 Model 2000 page
- Collection of old analog and digital computers at www.oldcomputermuseum.com
- The TRS-80 Model 2000 at Obsolete Computer Museum
- Tim Mann's TRS-80 Pages
- 8bit-Micro Online Tandy Support Group
- Semi-Virtual Diskette (SVD)
- Club100 (Model 100/102/200 Site)
- Model 100/102/200 site
- Blog concerning Superman advertising tie-in comic book for the TRS-80
