PDC Live

Observations

Here is a cleaned-up collection of some notes I made while trying to figure out what was going on. There is no definitive information here that isn't on one of the other pages. It is instructive to see what use (and abuse!) of the PDC system was occurring in July 1996.

Stream IDs

An illustration of BBC2's use of stream ID occurred while some portion of the late-night educational transmission "The Learning Zone" was being broadcast. This is billed as one item, running from 00:30 to 05:00, although it actually contains many Open University and other programmes. Here is an extract from the packet log as the programme changed, slightly prettified:

	01:24:43  s1 0 0 UNDEF  0 0  UK-BBC2 24/07 01:00 No info
	01:24:46  s0 0 0 UNDEF  0 0  UK-BBC2 24/07 00:59 No info
	01:24:47  s1 0 0 UNDEF  0 0  UK-BBC2 24/07 01:00 No info
	01:25:37  s0 0 0 UNDEF  0 0  UK-BBC2       RI/T  No info
	01:25:38  s2 0 0 UNDEF  0 0  UK-BBC2 24/07 01:24 No info
	01:25:38  s1 0 0 UNDEF  0 0  UK-BBC2 24/07 01:00 No info

I think this represents a programme that started at 01:00 running throughout on stream 1, a sub-segment which started at 00:59 stopping on stream 0, the stop being marked with the special date and time 00/15 30:63, and another segment starting at 1:24 on stream 2.

Special Flags in the Date and Time Fields

Occasionally you may notice that the date and time fields of the PDC transmission change from something sensible like 23/07 16:05 to some unlikely value, like 00/15 28:63. It is reported that these strange values are described in the EBU specification for PDC with some complexity. Certainly, the short descriptions I have received do not bear much resemblance to the use to which they are put:

	31:63    VCR obeys own timer
	30:63    Record Inhibit/Terminate
	29:63    Interrupt (pause) current recording
	28:63    Continue recording after interrupt

Without seeing the specification, it is not easy to determine what these actually do; it doesn't seem likely that the BBC2 could have had exactly the above interpretations in mind when they sent some of these:

28:63 "CONTINUE" occurs rarely: it appeared for 3 seconds on 25/7 at 17:47, a few minutes before the end of Neighbours. It was on the same stream (0) as the valid Neighbours code.
29:63 "INTERRUPT" has happened twice, both on 24/7: first at 09:53, between two programmes, just after both a 31:63 "TIMER" and a 30:63 "RI/T"; next at 16:30, again between two programmes, just after a 31:63 "TIMER".
30:63 "RI/T" occurs very often. It is usually between programmes or is sent a short while before the end of a programme.

31:63 "TIMER" also occurs often, and in much the same way as 30:63 "RI/T". However, I have also seen it sent repeatedly, as on 22/7, when it was broadcast during a block of unremarkable children's programmes. From this alone, I might have guessed that the code was the timer flag, meaning "I don't know the PDC for these". But look what happened on 23/7, for example:

    16:08:46-16:28:39  46  s1 0 0 UK-BBC2 23/07 16:05 Peter Pan
    16:29:32-16:30:45   5  s0 0 0 UK-BBC2 00/15 TIMER 
    16:32:45-16:55:05  62  s1 0 0 UK-BBC2 23/07 16:30 Ocean Odyssey
    16:55:58-16:57:11   3  s0 0 0 UK-BBC2 00/15 TIMER 
    16:58:40-17:07:59  77  s1 0 0 UK-BBC2 23/07 17:00 Newsround
    17:08:08-17:08:08   1  s1 0 0 UK-BBC2 00/15 RI/T  
    17:08:09-17:08:09   1  s0 0 0 UK-BBC2 00/15 TIMER
    17:08:10-17:08:10   1  s1 0 0 UK-BBC2 00/15 RI/T
    17:08:19-17:09:11   3  s0 0 0 UK-BBC2 00/15 TIMER
    17:10:33-17:34:00  48  s1 0 0 UK-BBC2 23/07 17:10 The Lowdown
    17:34:39-17:51:06   6  s0 0 0 UK-BBC2 00/15 TIMER Still Tourist
    17:55:15-19:26:44 221  s1 0 0 UK-BBC2 23/07 17:55 Film

Here 31:63 "TIMER" seems to be used just like the code 30:63 "RI/T", coming on for a short time at the end of the first two programmes (though always on a different stream---0 not 1). But then it gets interleaved with 30:63 "RI/T" after "Newsround", and broadcast throughout "Still a Tourist".

More details or ideas appreciated.

BBC2 Regional Opt-Outs

BBC2 was supposed to use the timer flag during regional opt-outs until the service was properly set up, but that hasn't been my experience! For example, although there was supposed to be a regional variation at 23:15 on 23 July 1996 and the PDC packets broadcast by Wenvoe went:

    22:31:37-23:15:57 486  s0 0 0 UK-BBC2 23/07 22:30 Newsnight
    23:16:12-23:16:12   1  s0 0 0 UK-BBC2 00/15 RI/T
    23:19:32-23:58:09   9  s1 0 0 UK-BBC2 23/07 23:15 Double Exp.
    23:57:53-00:17:38  11  s0 0 0 UK-BBC2 23/07 23:55 Weatherview
    00:32:05-00:55:41  56  s0 0 0 UK-BBC2 24/07 00:30 Learning Zone

According to the TV listing, Wales was supposed to opt out from Double Exposure and broadcast two programmes, one at 23:15 and one at 23:45. Then they should have rejoined at 23:55 when Weatherview was supposed to be on for 5 minutes---but the Weatherview code kept going for 30 minutes!

The next night was really confusing, with no opt-out and two codes that don't match up with anything advertised (although the second one is in Learning Zone).

    22:33:29-23:16:47 466  s1 0 0 UK-BBC2 24/07 22:30 Newsnight
    00:00:17-00:00:17   1  s1 0 0 UK-BBC2 24/07 23:55 not scheduled!
    00:00:45-00:00:45   1  s0 0 0 UK-BBC2 24/07 23:15 Double Exp.
    00:31:00-00:31:15   2  s0 0 0 UK-BBC2 25/07 00:28 not scheduled!

However, in both cases note that I get hardly any packets for hours. This might therefore be the fault of my receiving program, which is trying to get the BBC Micro Teletext Adapter to do something occasionally it doesn't normally do at all. Note also that the BBC2 service is supposed to be properly regional now (or soon if not already), so this issue is perhaps a matter of short-lived interest.

This page was created on 22 July 1996. It was last updated 31 August 1996.
Please send comments to Robin O'Leary pdc at ro dot nu