TRS-80

Overview

The TRS-80 is a desktop microcomputer put out by Tandy Corporation which was very popular in the 1970s and 1980s. TRS stands for Tandy Radio Shack, and the system is affectionately known as the "Trash 80" by fans. The microcomputer had important features such as a full keyboard, included monitor, well written floating point BASIC programming language, and a $600 price point. The computer was released in 1977, a couple years before Atari made games a driving factor for computer sales. As such, the TRS-80 was not generally a gaming platform and many games available for it use ASCII graphics or are simple text adventures. Sound was difficult to program, as was just about anything, so games with sound, such as Ball Turret Gunner, displayed it proudly on the box. The TRS-80s gaming problems were mostly fixed with the TRS-80 Color Computer (CoCo) line which launched 3 years later. As the line progressed through the late 80s, Tandy faded into obscurity as Commodore and Atari edged out ahead in gaming capability.

Technical Specifications

• CPU - Zilog Z80 1.77 MHz processor
• Memory - 4 Kb / 16Kb
• Video - 128 x 48 resolution, monochrome TV monitor as display
• Audio - None
• Media - Cassette tapes via built in drive, floppy disk via expansion
• Built-in Language - BASIC Level I / BASIC Level II
• Keyboard - QWERTY layout with 53 full-stroke keys
• OS - TRSDOS
• IO Ports - Monitor, cassette interface, expansion port

Hardware

The TRS-80 was released as a fully loaded microcomputer with a cassette drive, monitor, and keyboard. The basic model included a mere 4KB of RAM, while later models shipped with 16KB.

Keyboard

Data from the keyboard was read in a rather strange way on the TRS-80. The keys were mapped to pre-defined locations in memory and the computer would poll these locations to get the current state of the keyboard. The keyboards of the original TRS-80 models were generally regarded as poor as suffered from "keyboard bounce" which would result in duplicate letters accidentally being typed. To correct this problem, keyboard de-bounce software was distributed which made sure the keyboard wasn't polled too rapidly. This software was later build into the machine.

Video

Early TRS-80 models used a black and white RCA TV as a monitor, while later models switched to a more pleasant black and green. The TRS-80 could not display true, bitmap graphics, but instead used a subset of ASCII characters called semigraphics. The display featured 64 character columns with 16 character rows, and graphical software used ASCII characters and semigraphics. Semigraphics were characters formed as a grid of 2x3 blocks filled in 64 different ways. The 2x3 grid characters mapped out over the whole 64x16 display gave a virtual resolution of 128x48, all done with ASCII characters and semigraphics.

Cassette Drive

Programs were usually stored on cassettes, read by the built-in cassette drive. The tape deck included was just a standard monaural deck and the user had to manually set the volume while loading a program. If the volume was not correct while loading, the user would have to rewind, adjust the volume, and attempt to load again. Models with BASIC Level I read/wrote data at 25 bytes/sec, while models with BASIC Level II read/wrote data at 50 bytes/sec. No hardware controller existed for loading or storing data; the sounds were created electronically by switching the CPU voltage rapidly from negative to positive and back causing a click. Clicks were registered as 1s in the bit stream, while a silence was 0.

Expansion Interface

The TRS-80 expansion interface was an expensive but very useful option add-on that added a variety of features. They added 16k or 32k RAM, a second tape unit connector, a floppy disk controller, a printer port, a serial port, and a real time clock. The expansion interface was troublesome and was a leading cause of system crashes and lock-ups for a variety of reasons.

Models

Model I

In 1977, Tandy released the $599 Radio Shack TRS-80 around the same time as the Apple II and Commodore PET. It used a black and white RCA TV for a monitor, without a tuner. The Model Is were notorious for causing RF interference, so much so that some games were set up to output sound to an AM radio. The FCC eventually found the Model Is didn't comply with regulations and they were replaced with the Model III. Early Model Is had problems reading tapes from the cassette deck. The ROM was later modified to correct this, but users could get the problem fixed at a service center by having a small PCB installed.

Model II

The TRS-80 Model II was a business model released in 1979, and was completely different from the Model I. It featured a Zilog Z80A processor running at 4mhz, a Shugart 8" floppy drive, and an 80x24 monitor. The keybaord was detachable and it came with a standard printer port and 2 serial ports. Up to 4 floppy drives could be connected to one computer, each floppy holding 500k of data compared to the 87k of a Model I disk. The Model II used the TRSDOS-II operating system which made it largely incompatible with Model I software, and is thus considered a rather obscure TRS-80 model.

Model III

The Model III is the successor to the Model I and was released in 1981. It featured two 5.25" floppy drives that could convert Model I disks since difference in ROM made a few programs incompatible. The Model III also featured a better keyboard, build-in lowercase letters, and a faster processor: a Zilog Z80A running at 2.03mhz.

Model 4

The Model 4, released in 1983, includes two 5.25" drives, a 4mhz Zilog Z80 processor, and had an 80x24 resolution. It is fully backwards compatible with the Model III and emulates it perfectly. The Model 4 came with either 64KB or 128KB of RAM, and ran on TRSDOS 6.0, LDOS, or even CP/M. An upgrade kit for Model IIIs was released.

Clones

The TRS-80 was a moderately cloned computer seeing clones manufactured in South Africa, Hong Kong, North America, Brazil and Europe. A couple Model I clones, the Lobo Max-80 and LNW-80, even cloned the expansion interface. Some clones included all of the features of the Model III, while others improved the graphics of the Model I (Reducing TRS-80 compatibility). Tandy documented their computers and peripherals in very detailed diagrams in the system's manual, which may have been a factor in the amount of clones on the market. Unlike the ZX Spectrum, Tandy clones are no longer being manufactured anywhere in the world.

Games

The TRS-80 had a wide variety of games ranging across all genres. There were arcade ports, ports from other home computer games, and plenty of original titles as well. TRS-80 games are unique in their creative use of the semigraphics and low resolutions. Due to the various TRS-80 models, games were largely incompatible between systems, and as such there was no standard TRS-80 game that could be played on every TRS-80. Tandy garnered early support from big developers like Adventure International, SSI, and Avalon Hill.

Notable Games:

• Apple Panic
• Arkanoid
• Ball Turret Gunner
• Demon Seed
• Frogger
• Missile Attack
• Rear Guard
• Rogue
• Starcross
• The Witness
• Zaxxon
• Zork