VTR Clock
MDFS::Software.Video.VTClock Search

For the BBC Microcomputer, RISC OS and Windows™

VTClock Alan Pemberton wrote this programme in BBC BASIC in 1983 in order to allow a BBC Microcomputer to place a countdown and ident clock on video productions. The BBC Micro has a 625-line 50-field 1V composite video output which is suitable for feeding directly into a video tape recorder. It is also easily modified with a genlock board so that its signal can be fed synchronously into a video mixer.

I adapted it to run natively on RISC OS and also on Windows using BBC BASIC for Windows and Alan has given permission for it to appear here.

CLOCK2.EXE 93KWindows binary


The program allows the user to type in the production details on the slate. Use the cursor keys to move around within each box and Shift-Return to move to the next box. The countdown may be started at any ten-second point, and the take number is incremented automatically.

When the clock is at rest, the following keys are recognised:
  • 1 set the clock to 10 seconds
  • 2 set the clock to 20 seconds
  • 3 set the clock to 30 seconds
  • 4 set the clock to 40 seconds
  • > increment the TAKE number
  • < decrement the TAKE number
  • SPACE start the countdown
  • S lets you type in the SHOT box
  • P lets you type in the PROG box
  • D lets you type in the DATE box
  • F set Auto-Fade on/off
  • B Blank display before countdown starts
  • C Continue countdown
  • E exit the program
At any point pressing ESCAPE will display the menu.

The User Port is set to various values as the countdown progresses. These can be used to control external equipment.

Each line goes 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
Giving the following bit pattern:
  • 00000000 Before starting
  • 00000001 40s
  • 00000011 30s
  • 00000101 20s
  • 00000001 15s
  • 00001001 10s
  • 00011001 6s
  • 00111001 5s
  • 01111001 3s
  • 00000000 0s

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Last update: 13-Dec-2006