3 ms·

Just skimming the Wikipedia page, it sounds like almost all Teletext was read-only, which the entire protocol was designed around. But since you stressed their

by _Nat_ 5y ago

Just skimming the Wikipedia page, it sounds like almost all Teletext was read-only, which the entire protocol was designed around. But since you stressed their plans being "read-only", was there something else to it?

zapzupnz 5y ago
Read-only as in KeyFax was literally a broadcast image of Teletext, rather than actual Teletext. That way, people without a compatible set or decoder (everybody) could watch it. That had the knock-on effect of users not being able to call up a page at will; they had to wait until it was broadcast.
iso1631 5y ago
Normal teletext you select a page (typically a 3 digit number from 100 to 999, although hexadecimal pages also existed) Your decoder would then look at the vertical blanking lines with the data on, and wait for the page to match the one you selected. This could be fast (typically pages like 100 would be broadcast every second or so), or slow (page 693 might be sent once every 15 seconds) The decoder would then show it. The decoder would only need a 1 page memory. "Read only" teletext didn't include a decoder at all, it was the output of a decoder at the TV station which was sent via normal UHF means, typically with background music. As memory got cheaper, "Fast Text" was introduced, each page would have shortcuts to 4 more pages (red, green, yellow, blue). These would then be stored in the background when they were broadcast, so the decoder needed 5 pages of memory, but the experience of the user was much better as there was less waiting for the next page they'd usually want. This also allowed "hidden" pages like "35F" to be used. Towards the end of analog programming, teletext brought in on a PC capture card was stored and decoded by your media player. Computers obviously had enough memory to store every page so response was instant.
- mrvenkman 5y ago
  It was a great hack. ;)
- chaoticmass 5y ago
  I wonder-- is this why my Sony HT Receiver remote has four unlabeled buttons on it, colored Red, Green, Yellow, Blue?
iamtedd 5y ago
A better description is non-interactive.
- joezydeco 5y ago
  Yes. Thank you. Totally got that wrong.

by _Nat_ 5y ago

zapzupnz 5y ago

Read-only as in KeyFax was literally a broadcast image of Teletext, rather than actual Teletext. That way, people without a compatible set or decoder (everybody) could watch it. That had the knock-on effect of users not being able to call up a page at will; they had to wait until it was broadcast.

iso1631 5y ago

Normal teletext you select a page (typically a 3 digit number from 100 to 999, although hexadecimal pages also existed) Your decoder would then look at the vertical blanking lines with the data on, and wait for the page to match the one you selected. This could be fast (typically pages like 100 would be broadcast every second or so), or slow (page 693 might be sent once every 15 seconds) The decoder would then show it. The decoder would only need a 1 page memory. "Read only" teletext didn't include a decoder at all, it was the output of a decoder at the TV station which was sent via normal UHF means, typically with background music. As memory got cheaper, "Fast Text" was introduced, each page would have shortcuts to 4 more pages (red, green, yellow, blue). These would then be stored in the background when they were broadcast, so the decoder needed 5 pages of memory, but the experience of the user was much better as there was less waiting for the next page they'd usually want. This also allowed "hidden" pages like "35F" to be used. Towards the end of analog programming, teletext brought in on a PC capture card was stored and decoded by your media player. Computers obviously had enough memory to store every page so response was instant.

mrvenkman 5y ago
It was a great hack. ;)
chaoticmass 5y ago
I wonder-- is this why my Sony HT Receiver remote has four unlabeled buttons on it, colored Red, Green, Yellow, Blue?

iamtedd 5y ago

A better description is non-interactive.

joezydeco 5y ago
Yes. Thank you. Totally got that wrong.