VTR Clock


For the BBC Microcomputer and Acorn RISC OS

By Alan Pemberton

I wrote this programme in BBC BASIC in 1983 in order to allow a British Broadcasting Corporation Microcomputer to place a countdown and ident clock on video productions. The BBC Micro had a 625-line 50-field 1V composite video output which was suitable for feeding directly into a video tape recorder. It was also easily modified with a genlock board so that its signal could be fed synchronously into a video mixer. More recently I adapted the programme for an Acorn Archimedes computer under BBC emulation.

Interest was recently expressed on the uk.tech.broadcast newsgroup in a VTR Clock programme for a PC or Mac. However, there may be people who still have BBC Micros or RISC OS machines, and so I present my programme for those users to download.

The programme allows the user to type in the production details on the slate, and also to present some identification text in the space below the clock. The countdown may be started at any ten-second point, and the take number is incremented automatically. The screen can be arranged to fade to black automatically at the three-second point. Full instructions are shown on first running the programme, and help is available at any time by pressing escape.

BBC users should download the files CLOCKBAS and CLOCKSCR. Type CHAIN"CLOCKBAS" to load and run the programme.

If you have problems running the tokenised BASIC programme, try downloading CLOCKLIS, which is an ASCII listing. You can load that into the BBC Micro by typing *exec CLOCKLIS. Note that some REM and PRINT statements use characters in the range 128-255, which may not be transferred correctly, though that should not affect the running of the programme.

RISC OS users should download the zipped file VTR-Clock.zip.

Depending on the browser in use, it may be necessary to force the browser to save the link to disc, in source form, rather than simply clicking on the link.

If downloading is unsuccessful, and you desperately want a copy of this programme, please e-mail me me with your postal address and I will send you a copy on 3.5" 800K ADFS floppy or a CD-R. Unfortunately, I can no longer produce 5.25" BBC DFS floppies. I could also send a DOS or Macintosh floppy at a pinch.

Richard Russell has information about BBC Basic emulators for Windows on his website.

The instructions in the programme contain embedded teletext characters, which make the listing rather difficult to read. Here they are in plain ascii:


All the functions of this clock are available by pressing the appropriate key when the clock is at rest. Alternatively, a menu is displayed when ESCAPE is pressed.

In the DATE/PROG/SHOT modes, you use the machine as a video typewriter, within the chosen window. Use the cursor, return and delete keys as normal. To exit each box press SHIFT + RETURN.

When the clock is at rest, pressing

1 sets the clock to 10 seconds.
2 sets the clock to 20 seconds.
3 sets the clock to 30 seconds.
4 sets the clock to 40 seconds.
> increments the TAKE number.
< decrements the TAKE number.
S lets you type in the SHOT box.
P lets you type in the PROG box.
D lets you type in the DATE box.
E exits the program.
SPACEBAR restarts the countdown.
ESCAPE displays this menu.

Seven logic lines are provided on the User Port for the control of external equipment. These go to logical one as follows:

Bit 0 While the clock is counting.
Bit 1 From 30s to 20s.
Bit 2 From 20s to 15s.
Bit 3 From 10s to 0s.
Bit 4 From 6s to 0s.
Bit 5 From 5s to 0s.
Bit 6 From 3s to 0s.

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Compiled by Alan Pemberton
Sheffield, South Yorkshire, England
Email me