Atomic frequency standards and GPS receivers designed for precision timing are often equipped with an IRIG output.
A three-digit suffix specifies the type and frequency of the carrier, and which optional information is included: The recognized signal identification numbers for each format according to the standard 200-04 consist of: 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.
Thus, two marker bits in a row (P0 followed by Pr) marks the beginning of a frame.
Unassigned 9-bit fields between consecutive marker bits are available for user-defined "control functions".
IRIG standard 212-00 defines a different time-code, based on RS-232-style asynchronous serial communication.
IRIG J-1 timecode consists of 15 characters (150 bit times), sent once per second at a baud rate of 300 or greater: At the end of the timecode, the serial line is idle until the start of the next code.