TRS-80

The Radio Shack TRS-80 microcomputer (later called the Model I ) was announced on August 3, 1977 . It was the company's debut in the home computer market. The kit for $ 599 included a tape recorder and was the most expensive product ever sold at Radio Shack electronics stores. Store management was not confident in the computer market, so the original series was released in just 3000 copies. This quantity was ordered in such a way as to use computers for accounting needs in the stores of the network, if the TRS-80 had not been bought up. In the first month, 10,000 cars were sold, and 55,000 for the entire first year. Until the completion of production in January 1981, a total of 250,000 copies were sold. TRS-80 Model I.

In Model I, the motherboard and keyboard of the machine were combined in one package - this was the typical solution for 8- and 16-bit microcomputers of the time; the power supply, however, was external. The Zilog Z80 was used as the central processor at a frequency of 1.77 MHz (later models were supplied with the Z80A). The base model was originally shipped with 4 KB of RAM, and later with 16 KB.

Getting information about keystrokes was unusual for computers of the time. Instead of transmitting data about the pressed keys through the I / O port , the keyboard was displayed on the allocated memory area. When reading certain addresses from this area, it was possible to obtain information on the status of the corresponding group of keys.

The TRS-80 was packaged with a black and white CRT monitor , which was a converted black and white RCA XL-100 TV. The screen gave a light blue glow. Users often put on the screen green or yellow filters or replaced the kinescope in order to reduce eye fatigue. Later models came with a green monitor. Due to the limited bandwidth of the interface card installed on the TV instead of the radio receiving path, the image lost horizontal synchronization when large white areas were displayed on the screen; To correct this problem, a small revision of the scheme was required, which takes no more than half an hour of work.

The TRS-80 video controller supported text mode with 16 lines of 64 or 32 characters per line, and a low-resolution graphics mode of 128 × 48 pixels. Color not supported. The video memory was separate and had a volume of 1024 × 7 bits. The lower 6 bits determined the ASCII code of the symbol, or were displayed on the screen directly, in a grid of 2 × 3 blocks. The high bit was used to switch between text and graphic modes ^[2] . In later models, such as the TRS-80 Color Computer , a “semi-graphic” mode appeared in which low-resolution graphics were simulated using a special character set.

Any write operation in the video memory, both through the PRINT operator in BASIC, and directly, led to a blinking of the screen - this was a feature of organizing access to the common bus. This did not have a strong effect on BASIC programs, but for fast programs written in assembly language, this was already a serious limitation.

Standard monaural compact cassettes served as storage media for programs and user data. The package included a tape recorder Radio Shack CTR-41. The computer’s tape interface was very sensitive to changing the signal recording level, it was possible to understand that the correct level was set only by the flashing symbol on the screen, meaning that the data is being loaded - therefore, to find the correct signal level, you had to do a series of download attempts, rewinding the film each time and restarting the car. Users are used to writing the same data in a row several times, in the hope that one of the copies will be readable.

CoCo

Tandy also produced the TRS-80 Color Computer (CoCo) based on the Motorola 6809 processor . The car was aimed at the home market and competed with the Commodore 64 . OS-9 operating system was supplied with the machine - multi-user and multitasking.