8-26
24 Bit BCD Time Code*
* May be followed by 12 bits for day-of-year and/or 4 bits for figure-of-merit
  (FOM).  The FOM ranges from better than 1 ns (BCD character 1) to greater
  than 10 ms (BCD character 9).
Level
Held
Hi
Until
Start
of
Next
Code-
Word
Example:  Selected Time is 12:34:56
Level
Held
Hi
Until
Start
of
Code-
Word
20
msec
LLLH
8421
LLHL
8421
LLHH
8421
LHLL
8421
LHLH
8421
LHHL
8421
Hours
Minutes
Seconds
1
2
3
4
5
6
Rate:  50 Bits per Second
Bit Pulse Width:  20 msec
H = +6V dc ± 1V
L = -6V dc ± 1V
8
4
2
1
8
4
2
1
8
4
2
1
8
4
2
1
8
4
2
1
8
4
2
1
BCD Time Code
(MIL-STD-188-115)
   Time codes are used primarily to record time-of-day information with data in order to provide a time reference during data reduction (also called “time tagging”).  Time codes originated with requirements during early missile and space programs to correlate test data with precise time.  Today, time codes are used widely in applications such as communications systems, medical (patient monitoring) applications, and industrial and commercial data acquisition systems.


MIL-STD-188-115, Military Standard, "Interoperability and Performance Standards for Communications Timing and Synchronization Subsystems," 31 March 1986.  Copies are available from Naval Publications and Forms Center, 5801 Tabor Ave.,    Philadelphia, PA 19120

Parallel time codes are defined in IRIG Standard 205-87

Serial time codes are defined in IRIG Standard 200-98, http://tecnet0.jcte.jcs.mil/RCC/manuals/200/index.html