TRS-80 MC-10

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The TRS-80 MC-10

The TRS-80 MC-10 microcomputer is a lesser-known member of the TRS-80 line of home computers, produced by Tandy Corporation in the early 1980s and sold through their RadioShack chain of electronics stores. It was apparently designed as a low-cost alternative to Tandy's own TRS-80 Color Computer to compete with entry-level machines that had previously dominated the market, such as the Commodore VIC-20 and Sinclair ZX81.

Due to its limited feature set, the MC-10 was of value primarily to hobbyists and as an introduction to computer programming. It was not a commercial success and was discontinued only a year after its introduction.

A clone of the MC-10, the Alice, was marketed in France through a collaboration among Tandy, Matra, and Hachette.

[edit] Description

About the size of a hardcover book, the MC-10 came equipped with four kilobytes of RAM, a Motorola MC6803 eight-bit microprocessor, a built-in serial port, and graphics capabilities similar to those of the original Color Computer (provided by the same Motorola MC6847 video display generator).

Like most early home computers, the MC-10 included a BASIC interpreter in ROM and used regular audio cassettes for bulk storage. Text and graphics were displayed on a television set via a built-in RF modulator. Less common for machines in its class was the integrated RS-232 serial port, which allowed the MC-10 to use a wide variety of line printers and modems without additional hardware.

Even so, at the time of its release in 1983, the MC-10's specifications were underwhelming. Disk drives, full-travel keyboards, medium-resolution graphics, and complete 64-kilobyte memory banks were becoming popular features for home computers; the MC-10 offered none of these, severely limiting the functions it could perform and the range of users to which it could appeal. Even hobbyists did not seem drawn by its low price tag, although Tandy did little to spread the word that the machine was existed in the first place.

The MC-10 was discontinued in 1984, along with the 16 kB memory upgrade and small amount of cassette-based software that had been released for it. It never achieved a wide following.

[edit] Specifications

CPU: Motorola 6803 @ 0.89 MHz
RAM: 4 kB on-board, expandable to 20KB via external expansion pack
ROM: 8 kB (Micro Color Basic, developed by Microsoft)
VDG: MC6847
- Text: 32×16
- Low-res: 64×32, 8 color (4bpp)
- Low-res: 64×64, 4 color (2bpp)
- Med-res: 128×64, 2 color (1bpp)
- Med-res: 128×64, 4 color (2bpp)
- Med-hi: 128×96, 2 color (1bpp)
- Med-hi: 128×96, 4 color (2bpp)
- Hi-res: 128×192, 2 color (2bpp)
- Hi-res: 128×192, 4 color (2bpp) (required memory-pak)
- Hi-res: 256×192, 2 color (1bpp) (required memory-pak)
I/O Ports:
- RS-232C serial interface (300-9600 baud; 600 baud from BASIC)
- Cassette interface (1500 baud)
- Internal RF modulator
- Memory expansion interface

Although the memory expansion interface connected directly to the CPU bus and could have been used for many applications, the edge connector involved had an unusual number of pins and was difficult to obtain.

The RS-232C serial interface had extremely limited usefulness. Although the 6803 CPU conveniently includes a built-in UART, it was not connected to and did not assist the RS-232C interface in any manner. In part, this was because a single 3.58 MHz TV colorburst crystal was used to generate video and clock the CPU, and this clock rate did not correspond to any standard baud rate when divided for the UART. As a result, programs had to shift all bits individually into and out of the RS-232C interface, creating artificial and especially critical timing considerations.

The cassette interface had similar difficulties, plus a few. Although Micro Color Basic included an undocumented CLOADM command for loading machine-language programs and an undocumented VARPTR function for manipulating variables as memory, there was no corresponding CSAVEM command (documented or otherwise) to permit machine language programs to be saved to tape.