Data transmission

Statistical multiplexer A microcomputer-controlled data concentrator, the Micom Micro800, has been made available by Scicon Computer Services, UK, and is claimed to double the line capacity achieved with time-division multiplexers (TDM). An intelligent microprocessor control communicates with each channel and assigns the data rate to the channels as requ ired. Up to 16 asynchronous terminals can share a single telephone line. No changes to existing hardware or software are necessary. One or two synchronous channels can be multiplexed with the asynchronous channels. Built in self-test facilities are provided, and the multiplexer can be supplied for terminal speeds of 50-4 800 bit/s. A 'transparent' connection is provided for several remotely-located data terminals communicating concurrently on a single telephone line, or digital data link, with a central computer. Unlike a TDM, operation is designed to be free of errors. The multiplexer can buffer data prior to transmission, transmit data blocks whose length varies according to the loading on individual channels, check data blocks received on the highspeed line and request retransmission in the event of errors. Use of buffer storage can be made to accommodate temporary peak loading on individual channels, or group of channels, so that account can be taken of the average traffic loading on the high-speed line. The concentration or statistical multiplexing, achieved by buffer storage, results in increased channel capacity.

(Scicon Computer Services Ltd, Brick Close, Kiln Farm, Milton Keynes, MK 11 3El, UK. Tel: 0908 565656) []

common, so that a single input can be routed to 2, 4 or 8 different desinations. The PM12, for example, provides a bandwidth of 500 MHz and a risetime of 650 ps, an insertion loss at 100 MHz of 0.2 dB, and a VSWR of<0.2 dB (100 MHz). Crosstalk at 100 MHz is typically - 5 0 dB. All models have a characteristic impedance of 50 ~. The relay specification in all models is the same. Contact resistance changes from 200mS2 (max) closed to 1010 ~2 open; contact life expectancy at rated load is >3 x 106 operations. The maximum contact current is 250 mA with a resistive load. A relaydriver module can also be supplied to enable the reed switch to be driven directly from standard TTL level signals. (Microsystem Services, Duke

Street, High Wycombe, Bucks, UK. Tel: 0494 41661 Tx: 837187) []

Data transmission Fibre-optic duplex mains-powered datalinks are to be introduced by Rank Optics, UK. Signal input to the unit is via a standard 'D' type connector with TTL input and output levels. Each unit contains a receiver and transmitter unit, which converts the electrical impulses to optical signals and vice-versa. Units are operated in pairs to give full-duplex operation. The fibre-optic connection is made through AMP optical connectors provided as separate piece parts, or already terminated on to suitable fibreoptic cable. At a data rate of 10 Mbits, the standard system can be used at distances up to 700 m with Rank plasticclad silica fibre 250/PCS/2/20, or up to 1.5 km with fibre 250/PCS/2/08.

(Rank Optics, 200 Herehills Lone, Leeds, LS8 5QS, UK. Tel: 0532 624601)

[]

Reed switching Wide-band reed-switching modules, intended for routing high-frequency signals, have been made available by Microsystem Services, UK. The three modules (PM 12 (2-way), PM 14 (4-way), and PM18 (8-way)) contain 2, 4 or 8 reed switches. One contact of each is

vol 2 no3 june 1979

Business system A shared-logic word-processing system, intended to run in parallel with other applications, has been developed for

use with MCS, UK, Micos equipment. The unit is organized by books (limited by available disc storage), pages (up to 60 per book), lines (60 per page) and characters (70 per line). A table of contents is available, indexing being by pages and books. The Quote business computer is available with word-processing and ledger facilities. Uses include payroll, sales ledger, bought and nominal ledger, and file enquiries. The system includes 10 Mbyte of hard disc, a VDU, a 60 character/s printer and a 64 kbyte processor. (MCSMini-Computer Sys-

tems Ltd, Pork House, Pork Street, Moidenheod, Berkshire, UK. Tel." 0628 71411 Tx: 849434) []

Word processing A word-processing system to run on Data General equipment has been produced by Star Computer Group, UK. The Wordpro system allows wordprocessing and data-processing to be run concurrently, including direct access to data files. Written in Data General Business BASIC the system is compatible with the microNova, Nova and Eclipse ranges, and will support the DG 6053 terminal (for text entry and page editing) and the Diablo or Qume typewriter terminals (for text entry, lineby-line editing and text printing). Text-entry programs support both terminal types for rough copy to be entered into a disc file. A direct-entry program allows the terminal to be used like a typewriter, while an autoreturn entry program enables text to be keyed in a paragraph at a time, without carriage returns at the end of lines. The text is divided into lines of predefined length on completion of entry, prompting for hyphenation only when necessary. A line-oriented editor supports both types of terminals. A screen editor supports the DG 6053 VDU terminal which allows up to 24 80-character lines to be displayed and edited. One text-print program prints a text file once only. Another handles standard letters, printing and reprinting the same text but inserting different fields retrieved from data files held on disc. Both print programs handle underlining, centreing, automatic page numbering

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