Norpak Corporation was a company headquartered in Kanata, Ontario , Canada , that specialized in the development of systems for television-based data transmission . In 2010, it was acquired by Ross Video Ltd. of Iroquois and Ottawa , Ontario .
16-451: Norpak developed the NABTS (North American Broadcast Teletext Standard) protocol for teletext in the 1980s, as an improved version to the then-incumbent World System Teletext , or WST, protocol. NABTS was designed to improve graphics capability over WST, but required a much more complex and expensive decoder, making NABTS somewhat of a market failure for teletext. However, NABTS still thrives as
32-435: A television broadcast or video signal. In a normal NTSC video signal there are 525 "lines" of video signal. These are split into two half-images, known as "fields", sent every 60th of a second. These images merge on-screen, and in-eye, to form a single frame of video updated every 30th of a second. Each line of each field takes 63.5 μs to send; 50.3 μs of video and 13.2 μs amount of "dead time" on each end used to signal
48-541: A data protocol for embedding almost any form of digital data within the VBI of an analog video signal. Norpak's products, now part of and complementary to the Ross Video line, include equipment for embedding data in a television or video signal such as for closed captioning , XDS , V-chip data, non-teletext NABTS data for closed-circuit data transmission, and other data protocols for VBI transmission. This article about
64-553: A new use for the datacasting features of WebTV for Windows , under Windows 98 , as well as for the now-defunct Intercast system. Canadian company Norpak sold and manufactured encoders and decoders for NABTS until the end of analog broadcasting in North America in the early 2010s; it was acquired by the Ross Video consortium in 2010. NABTS is still used in legacy analog video systems for private closed-circuit data delivery over
80-588: A technological corporation or company is a stub . You can help Misplaced Pages by expanding it . This article about television technology is a stub . You can help Misplaced Pages by expanding it . This article about a Canadian corporation or company is a stub . You can help Misplaced Pages by expanding it . NABTS NABTS , the North American Broadcast Teletext Specification , is a protocol used for encoding NAPLPS -encoded teletext pages, as well as other types of digital data, within
96-473: A total of 172,800 bit/s, although 20% of that is needed for signaling purposes, so rates of 115,200 for end-user data are more typical. Applications requiring less throughput can simply use fewer lines. Horizontal blanking interval Horizontal blanking interval refers to a part of the process of displaying images on a computer monitor or television screen via raster scanning . CRT screens display images by moving beams of electrons very quickly across
112-709: The Telidon system. Similar systems had been developed by the BBC in Europe for their Ceefax system, and were later standardized as the World System Teletext (WST, aka CCIR Teletext System B), but differences in European and North American television standards and the greater flexibility of the Telidon standard led to the creation of a new delivery mechanism that was tuned for speed. NABTS
128-505: The vertical blanking interval (VBI) of an analog video signal. It is standardized under standard EIA-516, and has a rate of 15.6 kbit/s per line of video (with error correction ). It was adopted into the international standard CCIR 653 (now ITU-R BT.653) of 1986 as CCIR Teletext System C . NABTS was originally developed as a protocol by the Canadian Department of Communications , with their industry partner Norpak , for
144-550: The Horizontal blanking interval consists of: In the NTSC television standard, horizontal blanking occupies 10.9 μs out of every 63.6 μs scan line (17.2%). In PAL , it occupies 12 μs out of every 64 μs scan line (18.8%). Some modern monitors and video cards support reduced blanking , standardized with Coordinated Video Timings . In the PAL television standard,
160-551: The NABTS codes can be used on any of the 262 lines of the display, allowing up to 262 x 28 = 7,336 bytes of data per frame. Typically, however, the data is instead placed only in the unused lines of the vertical framing area. Lines 1–9 are used for vertical synchronization, line 21 is used for closed captioning , and everything after 22 is the television picture. That leaves 10 lines, lines 10 to 20, that are useful for sending data. At 60 fields per second, those 10 lines at 288 bits each encode
176-426: The blanking level corresponds to the black level , whilst other standards, most notably some variants of NTSC, may set the black level slightly above the blanking level on a pedestal or "set up level". Some graphics systems can count horizontal blanks and change how the display is generated during this blank time in the signal; this is called a raster effect , of which an example is raster bars . In video games,
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#1732894624919192-466: The frame. NABTS encodes data into the video signal as a series of dots at a fixed rate of 5.7272 Mbit/s. Each line of a field has 50.3 μs of video area that can be used for transmission, which results in 288 bits per line, or 36 bytes. In NABTS, three bytes are used for hardware synchronization, another three for the packet address, two for sequencing information, leaving 28 for data and redundant forward error correction (FEC) information. In theory,
208-570: The horizontal blanking interval was used to create some notable effects. Some methods of parallax scrolling use a raster effect to simulate depth in consoles that do not natively support multiple background layers or do not support enough background layers to achieve the desired effect. One example of this is in the game Castlevania: Rondo of Blood , which was written for the PC Engine CD-ROM which does not support multiple background layers. The Super Nintendo Entertainment System 's Mode 7 uses
224-476: The screen. Once the beam of the monitor has reached the edge of the screen, it is switched off, and the deflection circuit voltages (or currents) are returned to the values they had for the other edge of the screen; this would have the effect of retracing the screen in the opposite direction, so the beam is turned off during this time. This part of the line display process is the Horizontal Blank. In detail,
240-463: The television that the line is complete, known as the horizontal blanking interval (HBI). When the scanning process reaches the end of the screen it returns to the top during the vertical blanking interval (VBI), which, like the HBI requires some "dead time" to properly frame the signal on the screen. In this case the dead time is represented by unused lines of the picture signal, normally the top 22 lines of
256-474: Was the standard used for both CBS 's ExtraVision and NBC 's NBC Teletext services in the mid-1980s. The short-lived Time Teletext service, operated by the Time Video Information Services division of Time, Inc. and several experimental services launched by Boston's PBS station WGBH , also used NABTS. Due to teletext in general not really catching on in North America, NABTS saw
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