Re: Watching the numbers tick by
I seem to recall that each line of data (once decoded from the broadcast signal) started with the line number of the line - it meant that they could update 1 or 2 lines without having to send a full page, or if a page was mostly empty, they could just transmit the required lines preceded by a "clear screen" code.
[ this was useful for newsflash and subtitles ]
If the signal was dodgy, you could get lines appearing at the wrong position. Also, if a "clear screen" code was missed, you could get the next few lines that could be decoded appear as corruption over what was on the screen previously. And the main one was if the "switch to graphics character set" code was wrongly interpreted, the rest of the line could appear completely corrupted (each new line default to the normal character set until the alternate set was selected)
As an aside, the page number consisted of the first digit (whose name I forget, but it was something along the lines of a "magazine set number") - followed by a 2 digit hex number. (i.e. an 8 bit byte)
Effectively, the 2nd and 3rd digit was binary-coded-decimal, but Oracle did transmit pages not for direct public consumption using hex letters.
The display could be set by the broadcaster so that any pages outside the "magazine set number" you had selected would not appear in the updating first line.
This made it look cleaner when more than one "magazine sets" were multiplexed together from different sources... (oracle / tvam on itv, and oracle / 4-tel (?) on ch4)
I seem to remember a full whole page took less than 1K
Biting the hand that feeds IT
