National Instruments NI PXI-6682 User Manual

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Appendix B IRIG Protocol OverviewNI PXI-6682 Series User Manual B-2 ni.comtransmitted. This is usually specified by 3 digits that follow the IRIGstandard name (for instance, IRIG-B 120). Table B-2 details the differentcharacteristics of each IRIG option.For example, IRIG-B 120 indicates that the information is sent once persecond, 100 bits per second, on a 1kHz amplitude modulated sine wave,and that the information sent is the time of year in BCD, control bits, andthe seconds of day in straight binary seconds.There are 3 types of “bits” sent in the IRIG standard: binary zeroes, binaryones and position identifiers. To transmit a binary zero, the source mustkeep the signal at mark for 20% of the bit duration and at space for theremaining 80%; to transmit a binary one the source must keep the signal atmark for 50% of the bit duration and at space for the remaining 50%; totransmit a position identifier, the source must keep the signal at mark for80% of the bit duration, and at space for the remaining 20%. Binary bits areused to transmit information such as time of year, straight binary seconds,and so on, and position identifiers are used to separate the differentpieces of data transmitted. The second’s boundary is embedded into thetransmission by sending two consecutive position identifiers; the beginningof the second position identifier is the second’s boundary.Table B-2. IRIG Option CharacteristicsModulationtypeCarrier SignalFrequency Information sent0 Pulse width modulated 0 DC 0 TOY (BCD), CB, SBS1 Amplitude modulated(sine wave)1 100 Hz 1 TOY (BCD), CB2 Manchester modulated 2 1 kHz 2 TOY (BCD)3 10 kHz 3 TOY (BCD), SBS4 100 kHz 4 TOY (BCD), Year (BCD),CB, SBS5 1 MHz 5 TOY (BCD), Year (BCD), CB6 TOY (BCD), Year (BCD)7 TOY (BCD), Year (BCD),SBSCB = control bits