The

Mullard Mullard Limited was a British manufacturer of electronics, electronic components. The Mullard Radio Valve Co. Ltd. of Southfields, London, was founded in 1920 by Captain Stanley R. Mullard, who had previously designed thermionic valves (US ...

SAA5050 was a

character generator A character generator, often abbreviated as CG, is a device or software that produces static or animated text (such as news crawls and credits rolls) for keying into a video stream. Modern character generators are computer-based, and they can ...

chip for implementing the Teletext character set. Teletext PCB

The SAA5050 was used in

teletext Teletext, or broadcast teletext, is a standard for displaying text and rudimentary graphics on suitably equipped television sets. Teletext sends data in the broadcast signal, hidden in the invisible vertical blanking interval area at the to ...

-equipped television sets, viewdata terminals, and

microcomputer A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (P ...

s, most notably on computers like the Philips P2000 (1980), Acorn System 2 (1980),

BBC Micro The BBC Microcomputer System, or BBC Micro, is a family of microcomputers developed and manufactured by Acorn Computers in the early 1980s as part of the BBC's Computer Literacy Project. Launched in December 1981, it was showcased across severa ...

(1982), Malzak and the

Poly-1 The Poly-1 was a desktop computer designed in New Zealand for educational use. Background The Poly-1 was developed in 1980 by Neil Scott and Paul Bryant, who at the time were teaching electronics engineering at Wellington Polytechnic (now Massey ...

, and

Prestel Prestel was the Brand#Brand names and trademark, brand name of a videotex service launched in the UK in 1979 by BT Group#Post Office Telecommunications, Post Office Telecommunications, a division of the British Post Office Limited#History, Po ...

adapters like the AlphaTantel. This chip was also manufactured by

for

Philips Koninklijke Philips N.V. (), simply branded Philips, is a Dutch multinational health technology company that was founded in Eindhoven in 1891. Since 1997, its world headquarters have been situated in Amsterdam, though the Benelux headquarter ...

Operation

The chip generated appropriate video output for a 7-bit input

character code Character encoding is the process of assigning numbers to graphical character (computing), characters, especially the written characters of human language, allowing them to be stored, transmitted, and transformed using computers. The numerical v ...

representing the current character on the text line, while keeping track of the effect of any of the various

control character In computing and telecommunications, a control character or non-printing character (NPC) is a code point in a character encoding, character set that does not represent a written Character (computing), character or symbol. They are used as in-ba ...

s defined by the teletext standard that had previously occurred in that text line, which could be used to change the foreground and background colour, switch to or from the alternate block graphics character set, or various other effects. Level 1 teletext test

Full-screen resolution generated by the SAA5050 was 480 × 500 pixels, corresponding to 40 × 25 characters. Each character position therefore corresponded to a 12 × 20 pixel space. Internally each character shape was defined on a 5 × 9 pixel grid that was loosely based on the Signetics 2513 character ROM chip. This was then interpolated by smoothing diagonals to give a 10×18 pixel character, with a characteristically angular shape, surrounded to the top and to the left by two pixels of blank space. This gave a particularly stable and flicker-free arrangement on

interlaced Interlaced video (also known as interlaced scan) is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth. The interlaced signal contains two fields of a video frame captured consecutively. Th ...

displays. The alternate set of 2 × 3 block graphic characters were created on the same 12 × 20 pixel grid, so that the top two blocks were each 6 × 6 pixels, the middle two blocks each 6×8 pixels, and the bottom two blocks again 6 × 6 pixels (or two fewer in each direction, if the "separated graphics" control character had been sent). The pixels were usually displayed with a 1.33:1 or 1.2:1

aspect ratio The aspect ratio of a geometry, geometric shape is the ratio of its sizes in different dimensions. For example, the aspect ratio of a rectangle is the ratio of its longer side to its shorter side—the ratio of width to height, when the rectangl ...

to give a full display close to the standard 4:3 TV aspect ratio, effectively a 400 × 300 or 480 × 400 display.

Versions

Compared to other alternative chips, the SAA5050 implemented the original

World System Teletext World System Teletext (WST) is the name of a standard for encoding and displaying teletext information, which is used as the standard for teletext throughout Europe today. It was adopted into the international standard ITU-R, CCIR 653 (now ITU-R ...

teletext standard (''Level 1''), which had no provision to set black for the foreground text colour. Some alternative chips at the time did allow this, as became formalized in the 1981 CEPT videotex standard. In addition to the UK version, several variants of the chip existed with slightly different character sets for particular localizations and/or languages. These had part numbers SAA5051 ( German), SAA5052 ( Swedish), SAA5053 (

Italian Italian(s) may refer to: * Anything of, from, or related to the people of Italy over the centuries ** Italians, a Romance ethnic group related to or simply a citizen of the Italian Republic or Italian Kingdom ** Italian language, a Romance languag ...

), SAA5054 ( Belgian), SAA5055 (U.S.

ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...

), SAA5056 (

Hebrew Hebrew (; ''ʿÎbrit'') is a Northwest Semitic languages, Northwest Semitic language within the Afroasiatic languages, Afroasiatic language family. A regional dialect of the Canaanite languages, it was natively spoken by the Israelites and ...

) and SAA5057 (

Cyrillic The Cyrillic script ( ) is a writing system used for various languages across Eurasia. It is the designated national script in various Slavic, Turkic, Mongolic, Uralic, Caucasian and Iranic-speaking countries in Southeastern Europe, Ea ...

). The SAA5050 was later superseded by the SAA5243 CCT chip, integrating a similar teletext character generator with all previously separately implemented functions such as decoding, timing and video generation. It was controlled through I²C.

References

{{reflist

External links

SAA5050 data sheet

Bedstead
a font inspired by the SAA5050 character shapes Teletext Graphics chips

Operation

Versions

See also

References

External links