The chip generated appropriate video output for a 7-bit input character code representing the current character on the text line, while keeping track of the effect of any of the various control characters 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 block characters and colours
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 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).
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F
2
3
6
7
The pixels were usually displayed with a 1.33:1 or 1.2:1 aspect ratio to give a full display close to the standard 4:3 TV aspect ratio, effectively a 400 × 300 or 480 × 400 display.
Versionsedit
Compared to other alternative chips, the SAA5050 implemented the original World System Teletext 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),[6] SAA5052 (Swedish),[7] SAA5053 (Italian), SAA5054 (Belgian), SAA5055 (U.S. ASCII), SAA5056 (Hebrew) and SAA5057 (Cyrillic).
The SAA5050 was later superseded by the SAA5243 CCT chip, integrating a similar teletext character generator with all previously separately implemented functions such as decoding, timing and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.
^"Machine: AlphaTantel (alphatan)". Vas the Man’s Arcade.
^Born, Uwe. "IC SAA5051 datasheet". Semiconductor data tables.
^"SAA 5052, Tube SAA5052; Röhre SAA 5052 ID78631, IC - Integra". Radiomuseum.org.
External linksedit
Bedstead, a font inspired by the SAA5050 character shapes
January 01, 1970
mullard, saa5050, character, generator, chip, implementing, teletext, character, 1979, saa5050, card, acorn, eurocard, systemsprinted, circuit, board, used, philips, viewdata, unit, featuring, saa5050, character, generator, saa5050, used, teletext, equipped, t. The Mullard SAA5050 was a character generator chip for implementing the Teletext character set 1 A 1979 SAA5050 in a VDU card for Acorn Eurocard systemsPrinted circuit board used in a Philips Viewdata unit featuring a SAA5050 character generator The SAA5050 was used in teletext equipped television sets viewdata terminals and microcomputers most notably on computers like the Philips P2000 1980 Acorn System 2 1980 BBC Micro 1982 Malzak and the Poly 1 2 and Prestel adapters like the AlphaTantel 3 4 5 This chip was also manufactured by Mullard for Philips Contents 1 Operation 2 Versions 3 See also 4 References 5 External linksOperation editThe chip generated appropriate video output for a 7 bit input character code representing the current character on the text line while keeping track of the effect of any of the various control characters 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 nbsp Level 1 teletext block characters and colours 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 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 0 1 2 3 4 5 6 7 8 9 A B C D E F 2 nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp 3 nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp 6 nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp 7 nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp nbsp The pixels were usually displayed with a 1 33 1 or 1 2 1 aspect ratio to give a full display close to the standard 4 3 TV aspect ratio effectively a 400 300 or 480 400 display Versions editCompared to other alternative chips the SAA5050 implemented the original World System Teletext 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 6 SAA5052 Swedish 7 SAA5053 Italian SAA5054 Belgian SAA5055 U S ASCII SAA5056 Hebrew and SAA5057 Cyrillic 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 See also editTeletext character set Viewdata Character generator AlphaTantel Philips P2000 Acorn System 2 BBC Micro Poly 1References edit SAA5050 Series Teletext Character Generator PDF Mullard 1982 SAA5050 Teletext Character Generator Vas the Man s Arcade Graham Adrian AlphaTantel Viewdata Terminal Binary Dinosaurs Retrieved 2023 05 02 Graham Adrian AlphaTantel Viewdata Terminal Motherboard Binary Dinosaurs Machine AlphaTantel alphatan Vas the Man s Arcade Born Uwe IC SAA5051 datasheet Semiconductor data tables SAA 5052 Tube SAA5052 Rohre SAA 5052 ID78631 IC Integra Radiomuseum org External links editSAA5050 data sheet Bedstead a font inspired by the SAA5050 character shapes Retrieved from https en wikipedia org w index php title Mullard SAA5050 amp oldid 1173311717, wikipedia, wiki, book, books, library,
