The sound department acts as the timecode master, and generates timecode which uses the time of day as a value, and a time base matching the project frame rate. Twenty-four hours of time will translate into twenty-four hours of time code.
Timecode is fed to the camera via the TC connector. The timecode source must be set in the camera to Ext LTC and the mode to Free Run. The project fps setting must match both the sensor frame rate and the time base of the external timecode signal. The camera can be set to use Jam sync generator, in which it samples the timecode value once and then continues counting based on its own high-precision crystal clock.
The timecode source can be disconnected from the camera after jamming in Jam sync generator mode. This mode ensures stable timecode with an offset of less than one frame for each eight hours, after which the camera has to be re-jammed.
Alternatively, the camera can be set to regenerate mode, or Regen on the TIMECODE OPTIONS screen. In Regen mode, the camera uses the timecode value of the external timecode source. This ensures correct timecode for an infinite duration, but the timecode source must remain connected to the camera.
Note that the camera ignores external timecode during record and counts using its internal clock to avoid timecode jumps should connection problems arise, e. g. due to a faulty timecode cable.
Variations: If shooting starts close to midnight, the timecode might be started with an offset time of day to prevent a rollover at midnight.
Restrictions: External timecode is only possible if the camera is running at sync-sound speed. If the camera is over- or undercranking, the timecode frame rate will no longer match the sensor frame rate, and timecode values would either be duplicate or dropped. To prevent this, the ALEXA will automatically switch to Int TC source and Regen mode when the sensor frame rate is changed.