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FarmerPotato

TI's chipset for UK Teletext and US Closed Captioning

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I'm going through Electronics magazine, a trade journal that covered business computers, semiconductor and software technology, and some consumer electronics. It's available on bitsavers.org, along with Datamation and Mini-Microcomputer Systems.


I found this interesting because I've never seen these part numbers in the 80s databooks. They must have been B2B only--this article mentions 100,000 first shipped to Sanyo. It also says the chipset is fabricated in I2L--the technology used for the SBP9900 military version. SBP 99xx chips (but not these) are found in TI's Bipolar Microcomputer Components Data Book for Design Engineers (I read 1981 3rd Ed) and that's a story to itself. 


Chips shown in the diagram:

 

SN94310N Video Processor: takes composite video, outputs signals and text (serial)
SN94311N Character ROM: 5x9 character definitions
SN94312N Serial-to-parallel converter (probably a renamed LS595 or such)
SN94313N Rounding Logic: said to smooth out character pixel edges
SN94314N Display Controller: Stores character codes in 8K RAM. Sends 4-bit row address to ROM.
SN94315N Timing Logic: Takes HSYNC and dot clock, clocks serial data and other.
SN94316N Output Logic: Reads character from RAM, sends 10-bit column address to ROM, integrates rounding 
         info, and finally generates RGB and Luminance signals.

 

 

Chip set captions TV programs for deaf

[Electronics, Jan 17, 1980, p. 41-42]


Beginning this spring, deaf and hard-of-hearing TV viewers will gain new
access to prime-time programming, thanks to a captioning project that
depends on a custom chip set developed by Texas Instruments Inc. The
captions will be visible only on specially equipped TV sets.


Project. The Federally sponsored project calls for digitally encoded
subtitles corresponding to a program's soundtrack to be transmitted on
line 21 of the TV vertical blanking interval. A new nonprofit agency
known as the National Captioning Institute will put the caption infor-
mation on floppy disks for network use with videotape equipment. TI
developed the seven-chip caption decoder over atwo-year period under
contract to the Public Broadcasting System. With speed and linear
requirements in mind, it uses a variety of bipolar techniques, notes L.
Dwain Chaffin, advanced circuits department manager at the company's
Sherman, TX plant.

 

2081433505_TIClosedCaptioningChipset.thumb.png.0e9d85a22252db4ae2169a8ebd17da9d.png


The heart of the system is the display controller, which combines linear
bipolar circuitry with integrated injection logic on a
47,000-square-mil chip. The controller works in conjunction with a
linear video processor chip and a 5,760-bit read-only-memory chip that
stores the captioning characters. (see figure above).


The ROM is made with Schottky TTL, primarily for speed, says Chaffin.
Each of the 96 ASCII and 8 special characters is stored in 45 bits, and
access time is 280 nanoseconds. The 250-milliwatt typical power
dissipation is low in view of the quantity of circuitry on the
18,000mil^2 ROM, Chaffin observes.


Other devices in the chip set are four low-power Schottky parts that
handle such functions as timing and output logic and "rounding" logic to
make characters easier to read. Chaffin says TI drew upon earlier
development work for its Teletext chip set for the British video
information system.


Prices. Without the chip set, the $249.95 retail price for decoder
units would be more than double, he adds. Sears Roebuck and Co. is the
sole distributor for these adapters and for the 19-inch color TV
receivers to incorporate the circuitry. To be available next fall, the
receivers will cost around $500, with about $100 attributable to the
built-in captioning circuitry.


Sanyo Electric Co. of Japan is making both adapters and TV sets for
Sears. TI is shipping 100,000 chip sets to Sanyo.


The Public Broadcasting System initiated work on the captioning project
in 1972, under contract with the Department of Health, Education and
Welfare. The National Captioning Institute, in Falls Church, Va., is
currently operating under HEW grants, but will receive an $8 royalty for
each adapter and receiver sold and will charge networks $2,000 per
program hour for the coded floppy disks. In addition to proprietary
rights to the circuits, the Public Broadcasting Service turned over to
the institute 20 Z80-based editing consoles and associated captioning
software. As well as the public network, ABC and NBC will participate
beginning in March with a total of 19 hours of weekly programming. More
programming will come later.   -Wesley R. Iversen


 

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Interestingly enough, that article was also the only hit I found for the chipset, using several different sets of search terms. . .

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 This might be the stand-alone decoder:

 

Sears Solid-State Telecaptioner, 1980.

Smithsonian Institute, EveryBody: An Artifact History of Disability in America

 

The Electronics article mentions Sears' receiver selling for $249.

 

 

Here is a Sears catalog page advertising the decoder, and the "Solid State" TV set with the decoder built-in.

 

Sears 1980 Catalog page: NBC, ABC, PBS, At Least 20 Hours a Week of Captioned Programs

 

An eBay sale listed this as a model 564 television. I got curious why quite a few Sears products were labeled "Solid State" in the 1980s. Because we saw TI advertise "Solid State Software Module" to "Solid State Cartridge". Meaning, there were no gas-filled vacuum tubes inside!

 

 

Here is Meryl Evans' blog about Types of Video Captions that shows it.  (She also remembers the TeleCaption 400 that came later.)

 

 

Edited by FarmerPotato
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