IRIG Timecode - IRIG J Time Code

IRIG J Time Code

IRIG standard 212-00 defines a different time-code, based on RS-232-style asynchronous serial communication. The time code consists of ASCII characters, each transmitted as 10 bits:

  • 1 start bit
  • 7 data bits
  • 1 odd parity bit
  • 1 stop bit

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

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

DDD:HH:MM:SS
  • SOH is the ASCII "start of header" code, with binary value 0x01.
  • DDD is the day of year, from 1 to 365 (or 366 in leap years).
  • HH, MM and SS are the time of the start bit.
  • The code is terminated by a CRLF pair.

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

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

DDD:HH:MM:SS.S

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

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

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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