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TRS-80

TRS-80 (also affectionately known as Trash-80) was the designation for several lines of computer systems produced by the Tandy Corporation and sold through its Radio Shack[?] stores in the late-1970s and 1980s.

Table of contents

Z80 Based Home Systems

The Tandy TRS-80 model I was Tandy's entry into the home computer market. It looked like a very thick keyboard (like the later Commodore VIC-20) and used a Zilog Z80 processor.

There were two versions of BASIC produced for the Model I. Level I Basic fit into 4K ROM, and Level II Basic fit into 12K ROM. The base machine was available with either 4K or 16K of RAM. Level I was integer only and had a smaller set of commands. Level II introduced floating point support, 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 coded in-house by Tandy, and Level II BASIC was licensed from Microsoft.

The Disk Based BASIC added the ability to disk I/O, and in some cases (NewDos/80, MultiDOS, DosPlus, LDOS) added powerful sorting, searching, full screen editing, and other features.

Microsoft also marketed a tape-cassette based enhanced BASIC called Level III Basic.

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, and green and amber filters or replacement tubes, to make the display easier on the eyes, were a common after market item.

The video hardware could only display text at a 64 characters by 16 lines resolution in upper case. This was because the video memory system only was 7 bits wide. Aftermarket Lowercase upgrades (which were very popular and referred to as the "Electric Pencil Modification" after a popular Wordprocessor of the time) added the 8th bit and through use of a switch, one could go back and forth between the original 7 bit or 8 bit video.

Primitive graphics could be displayed because 64 characters of the character set displayed as a grid of 2x3 blocks. Writing to the screen caused "snow" on the screen because no bus arbitration logic was used to arbitrate between CPU writes to the screen RAM and display logic reads from the same RAM. 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 very addictive arcade type games were available for the Tandy TRS-80.

User data had to be stored on cassette tape. To upgrade to a floppy disk based system you had to buy the "Expansion Interface" 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 seperator", and was thus very unreliable. There was also the ability to expand to up to 32K more RAM, a serial interface (option) and a centronics printer interface.

A Data Seperator and/or a Double Density disk controller (based on the WD 1773 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 Seperator. The LNDoubler added the ability to read and write from 8" Diskette Drives for over 1.2mb of Storage.

The resulting system was considered usable as a SOHO solution.

Many users complained about the TRS-80 keyboard which were mechanical switches and suffered from "Keyboard Bounce" resulting in multiple letters being typed accidentally. A Keyboard De-Bounce tape was distributed, which slowed down polling of the keyboard to compensate. Eventually, this was added to a later ROM revision.

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 was modifed to correct this.

Many clones of the TRS-80 Model I came on the market, including the LOBO Max-80 (Lobo also produced their own version of the Expansion Interface), the LNW-80 Model's I/II and Team Computers (LNW also produced an alternate version of the Expansion Interface), the Dick Smith System-80 sold in Australia and New Zealand (also sold as the PMC-80 in North America) and the Dutch Aster CT-80.

Tandy sold the LNW-80 computers with a Tandy Brand in Mexico.

In 1980, Tandy produced the Model II which was designed as a business machine. It was not an upgrade of the Model I, but an entirely different system. The Model II was built using the faster Z-80A chip and contained a built-in 8-inch floppy disk drive, as well as 64k of memory.

The Model II was later enhanced and became the Model 16, which was a more advanced business computer.

As a follow on to the Model I, 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 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 interferance. 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 successor to the Model III was the Model 4, which included the capability to run CP/M. The Model 4 also came in a "luggable" version known as the Model 4P which was portable. It was a self-contained unit That looked like a small sewing machine.

The Model 4 also had the ability to display high-resolution graphics with an optional board.

Business Systems

Tandy later came with the TRS-80 model 16, which was a follow on to the Model II. It was UNIX based (it used Microsoft's Xenix) 16 bit system (68000 plus Z80). Later computers in this line were the model 12 and model 6000. 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.

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

TRS-80 Model 100 line

In addition to the above, Tandy produced the TRS-80 Model 100 series which were the first commercial line of laptop computers. These were popular with journalists.

TRS-80 MC-10 line

This short lived and little known line of Tandy Computers was similar in appearance to the Sinclair ZX-81.

It was a small system based on the 6803 Processor and featured 16k of RAM. A 16k RAM Expansion pak was offered as an option.

TRS-80 Pocket Computers

TRS-80 was also used for a line of Pocket Computers which were manufactured by Sharp.

Tandy PC-Compatible Computers

In the early-1980s, Tandy began producing a line of computers that were more or less PC compatible. These systems were referred to as Tandy 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 Tandy 2000 system was similar to the Texas Instrument PC-Clone 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 T/I) 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.

For more information on the TRS-80 see http://www.trs-80.com



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