IRIG timecode: Difference between revisions

Revision as of 19:19, 17 October 2019

Revision as of 14:51, 13 November 2019

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'''Inter-range instrumentation group time codestimecodes''', commonly known as '''IRIG time codestimecode''', are standard formats for transferring timing information. Atomic frequency standards and GPS receivers designed for precision timing are often equipped with an IRIG output. The standards were created by the Tele Communications Working Group of the U.S. military's [[Inter-Range Instrumentation Group]] (IRIG), the standards body of the [[Range Commanders Council]]. Work on these standards started in October 1956, and the original standards were accepted in 1960.

The original formats were described in IRIG Document 104-60, later revised and reissued in August 1970 as IRIG Document 104-70, upgraded later that year as the IRIG Document to the status of a Standard, IRIG Standard 200-70. The latest version of the Standard is IRIG Standard 200-16 from August 2016.

== Time codesTimecodes ==

The different timecodes defined in the Standard have alphabetic designations. A, B, D, E, G, and H are the standards currently defined by IRIG Standard 200-04.

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{|class="wikitable"

|+IRIG time codetimecode

! Code || Bit rate || Bit time || Bits per frame || Frame time || Frame rate

|-

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Thus the complete signal identification number consists of one letter and three digits. For example, the signal designated as B122 is deciphered as follows: Format B, Sine wave (amplitude modulated), 1 kHz carrier, and Coded expressions BCDTOY.

The most commonly used of the standards is IRIG B, then IRIG A, then probably IRIG G. Time codeTimecode formats directly derived from IRIG H are used by [[National Institute of Standards and Technology|NIST]] [[radio station]]s [[WWV (radio station)|WWV]], [[WWVH]] and [[WWVB]].

For example, one of the most common formats, IRIG B122:

:IRIG B122 transmits one hundred pulses per second on an amplitude modulated 1 kHz sine wave carrier, encoding information in BCD. This means that 100 bits of information are transmitted every second. The time frame for the IRIG B standard is 1 second, meaning that one data frame of time information is transmitted every second. This data frame contains information about the day of the year (1–366), hours, minutes, and seconds. Year numbers are not included, so the time codetimecode repeats annually. [[Leap second]] announcements are not provided. Although information is transmitted only once per second, a device can synchronize its time very accurately with the transmitting device by using a [[phase-locked loop]] to synchronize to the carrier. Typical commercial devices will synchronize to within 1 microsecond using IRIG B timecodes.

== Time codeTimecode structure ==

IRIG time codetimecode is made up of repeating frames, each containing 60 or 100 bits. The bits are numbered from 0 through 59 or 99.

At the start of each bit time, the IRIG time codetimecode enables a signal (sends a carrier, raises the DC signal level, or transmits Manchester 1 bits). The signal is disabled (carrier attenuated at least 3×, DC signal level lowered, or Manchester 0 bits transmitted), at one of three times during the bit interval:

* After 0.2 of a bit time, to encode a binary 0

* After 0.5 of a bit time, to encode a binary 1

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Unassigned 9-bit fields between consecutive marker bits are available for user-defined "control functions". For example, the [[IEEE 1344]] standard defines functions for bits 60–75.

== IRIG Time Codetimecode ==

{|class=wikitable style="text-align:center;"

|+ IRIG A time code structure

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{{Clear}}

==IRIG J time codetimecode==

IRIG standard 212-00 defines a different time-code, based on [[RS-232]]-style [[asynchronous serial communication]].

The time codetimecode consists of [[ASCII]] characters, each transmitted as 10 bits:

* 1 start bit

* 7 data bits

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The on-time marker is the leading edge of the first start bit.

IRIG J-1 time codetimecode consists of 15 characters (150 bit times), sent once per second at a baud rate of 300 or greater:

<nowiki><SOH>DDD:HH:MM:SS<CR><LF></nowiki>

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* The code is terminated by a [[Newline|CR+LF]] pair.

At the end of the time codetimecode, the serial line is idle until the start of the next code. There is no idle time between other characters.

IRIG J-2 time codetimecode consists of 17 characters (170 bit times), sent 10 times per second at a baud rate of 2400 or greater:

<nowiki><SOH>DDD:HH:MM:SS.S<CR><LF></nowiki>

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This is the same, except that tenths of seconds are included.

The full-time codetimecode specification is of the form "IRIG J-''xy''", where ''x'' denotes the variant, and ''y'' denotes a baud rate of 75×2^''y''.

Normally used combinations are J-12 through J-14 (300, 600, and 1200 baud), and J-25 through J-29 (2400 through 38400 baud).

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== External links ==

* [http://www.meinberg.de/english/info/irig.htm IRIG information]&nbsp;— IRIG information page with diagrams

* {{Citation |title=The IRIGB standard site - The site dedicated to IRIGB standard Time code|url=http://irigb.com }}

[[Category:Timecodes]]