Time Codes

Time Codes

Time Codes, generally in serial form, are used to convey time information from one point to another. Many different time code formats have been developed over the years, by both commercial and military agencies. Many ESE products support one or more of these time codes as a standard feature; we can also address less common formats on a custom basis. Here is a description of the more common formats:

ESE Time Code™

ESE Time Code™ was originally developed in the mid 70's as an inexpensive way to send time of day to remote digital slave displays. The original format, TC76™, was capable of sending six digits of time data, or four digits of elapsed timer data (using a slightly altered bit format). The time can be sent in 12 or 24 hour format. No AM/PM data is sent in 12 hour mode, however. The newer, TC89™ time code adds two bits of information to convey AM/PM and display mode information. TC89 is compatible with old non-microprocessor slaves, although the older slaves don't recognize the mode bits. Subsequent to this, TC90™ time code was developed to take advantage of the new microproceesor based slaves. It is not compatible with the old slaves, but provides both Time and Date, and Auxiliary data when required. The ES160A and ES185A provide both TC89 and TC90 codes on separate connectors. With a few exceptions, TC89 is the standard output on most other products which feature ESE output.

SMPTE LTC & EBU Time Codes

SMPTE LTC & EBU time codes are used by the video & audio industries for providing frame-accurate time references for editing video & audio, or as a master time reference for radio / TV stations. When used for editing, the code is typically recorded on a spare audio or time code track on the tape. SMPTE (Society of Motion Picture & Television Engineers) code runs at 29.97 frames/second; EBU (European Broadcasting Union) code runs at 25 frames/second. These codes send Hour, Minute, Second and Frame data. SMPTE or EBU "LTC" (Longitudinal/Linear Time Code) is basically audio in nature. Another variety of these editing codes known as "VITC" (Vertical Interval Time Code or "vit-see") is video in nature; it is recorded on unused lines in the Vertical Interval of the video signal. ESE manufactures a number of VITC products, primarily for military clients; we can support VITC for other applications on a custom basis.

IRIG Time Codes

The Inter-Range Instrumentation Group codes, originally developed for sending time or other data around missile test ranges, finds use in government, military and commercial fields. These digital codes are typically amplitude modulated on an audio sine wave carrier (though not always). The most common version is IRIG-B, which sends Day of Year, Hour, Minute and Second data on a 1000 Hz carrier, with an update rate of one second. Other "IRIG" codes, as well as related codes such as "NASA", "XR3" and "2137" can be supported on a custom basis.

ASCII Time Code

ASCII Time Code is simply time data sent in serial ASCII form using either an RS-232 or RS-422 interface. It is typically used for interfacing time data to a computer (ESE provides software for synchronizing the clock of a PC computer to ESE Master Clocks). The data format & baud rate can vary depending on the product or intended application.

Network Time

Network-based time protocols such as NTP and PTP are increasingly popular for synchronizing equipment, or delivering accurate time to visual displays. NTP (Network Time Protocol) has been used for some time for this purpose, while the newer IEEE-1588 PTP (Precision Time Protocol) offers superior accuracy measured in nanoseconds. These data streams can typically be carried on common Ethernet networks.