KEY PRIORITIES
Another vital function of the syscon is to assign priorities and prevent conflicting functions being keyed. Timer systems are pre-programmed to reject impossible requests like ‘record for twelve hours’, ‘record two programmes at once’ or ‘stop recording before start time’; attempts to pre-programme a recording on a tabless cassette will result in eject function. Similarly, such mechanically destructive orders as ‘pause’ during rewind mode, and pointless commands like ‘search’ during record mode are rejected. In most machines, pressing two keys simultaneously will have no effect on the function (if any) in progress; obvious exceptions are record + play, audio dub + play and play + still. A typical mode shift table for a mains machine is given in Table 16.1.