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Old 05-11-2018, 03:49 PM
Foone Foone is offline
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Closed caption generator chips?

Hi, I'm doing some work with extracting bitmaps from character generator chips like those used in closed captioning from the 90s. I've currently got three:

STM STV5730A:


Maxim MAX7456:


And Mullard SAA5050:

(Not super accurate yet, cause it does some internal smoothing)

I'm looking for the names of similar chips, as they usually have the bitmaps in the datasheets. I'm specifically looking for ones used in closed captioning, these tend to be more for VCR displays and such, which limits the number of characters they implement.
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Old 05-11-2018, 04:03 PM
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Electronic M Electronic M is offline
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My telecaption vr-100 decoder box has ITT NCI LN21 G010279.000 3224.20, a brandless KA2919 236A, and some smaller 74 series logic and other chips that I'd guess are op-amps and such.
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Old 05-11-2018, 04:03 PM
user181 user181 is offline
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I don't have anything. Is this for some kind of project you're working on, or is it just research?
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Old 05-11-2018, 04:13 PM
Foone Foone is offline
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It's for a software project I'm working on which lets you generate closed caption images.
I'm converting the rom contents to bitmaps for placing over screencaps.

I'm just trying to find specific chip types that were used during this time to make it accurate (rather than just getting an arbitrary similar looking font)
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Old 05-11-2018, 09:29 PM
Chip Chester Chip Chester is offline
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There are a few various decoder fonts out there in TrueType, and a few more 'locked away' in long-discontinued decoder chips. Built-in decoders in sets used caption decoder chips in the early years, then 'graduated' to using the same chip used with on-screen menus. Sony and Trinitron Akai used the best-looking fonts of the day. The 'no descender' fonts (shown in your post) are kind of the classic, so-ugly-they're-cute fonts.

When you 'extract' these, is it destructive to the set/decoder, or to the chip? Or could you work with a digital file of the on-screen presentation of all the characters, as brought forth by the caption encode/decode process?

I have a collection of good, bad, and fantastic caption decoders (and similar devices) from the past 25 years or so. Also have equipment to generate and harvest both 608 and 708 caption data in any format. Don't overlook the nice-looking caption fonts in QuickTime, too... In pro broadcast hardware, EEG has some great-looking decoders. Evertz has some lousy ones. They both cost $3000.

Most current-day caption displays are driven via graphics chips within the set-top box, be it cable, satellite, or OTT/AppleTV/Roku-type device. The internal caption decoder in current sets is only used with over-the-air broadcasts, since the HDMI cable spec has no 'lane' for caption data at all.

As captioning progressed over the years, the allowable character sets expanded as well. First-generation was pretty limited, with barely enough character set support for English, Spanish, French, etc. Later versions (Telecaption II compatible stuff) expanded that set a bit, but limitations still existed. Limitations, like decoders couldn't display an asterisk *, for example, not because of chip limitations, but it was an 'illegal' character in caption data. Once HD/708 captions hit the scene, there was no practical limit to characters, and fonts/attributes were more in the hands of the viewer, and varied by set manufacturer/graphics chip design.

- Chip
(Closed-captioner for 25+ years. Feel free to PM me if you'd like.)

Last edited by Chip Chester; 05-11-2018 at 09:36 PM.
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Old 05-12-2018, 07:04 AM
kf4rca kf4rca is offline
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How about the 2513 chip made by Signetics and GI? Sometimes called RO3-2513. There are several versions out there depending on what alphabet you get. (You can even get it with Kata Kana).
The newest version uses only one 5 V supply but the older ones used +5,-12, and +12.
Not pin for pin compatible.
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Last edited by kf4rca; 05-12-2018 at 07:11 AM.
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