Subchannel numbering: CH10 vs. TMATS
This issue was solved in IRIG106-15 but still has to be considered for recorders conforming to older releases or using older TMATS. The end of the section presents the solution in the 2015 release.
Some data types have subchannels and some of these have additional attributes that are described in TMATS. To map the TMATS attributes to the subchannel, subchannel numbers are used. Depending on the recorder vendor TMATS and CH10 might use different numbers to describe the same subchannel. This sometimes even deviates within vendors (possibly by recorder model / firmware). The data types where conflicts have been seen start their numbering with 0 in CH10 and with 0 or 1 in TMATS.
The table below shows all data types where subchannels exist and the lowest numbers in CH10 and TMATS
|Data type||Lowest CH10 subchannel number||Lowest TMATS subchannel number|
|Analog (0x21)||1 (0 means 256)||TMATS does not explicitly state the subchannel numbers (see CR80 2.1)|
|Message (0x30)||0||0 or 1 (R-x\MSCN-n-m)|
|ARINC 429 (0x38)||0||0 or 1 (R-x\ASN-n-m)|
|UART (0x50)||0||0 or 1 (R-x\USCN-n-m)|
|Ethernet (0x68)||0||0 or 1 (R-x\ENBR-n-m)|
|CAN (0x78)||0||0 or 1 (R-x\CBN-n-m)|
Note: Actual problems have been seen on ARINC 429, UART and Ethernet. Problems on Message and CAN data types are expected but not confirmed.
Since IRIG 106-15 the issue has been solved like this: CH9 now requires all declared subchannel numbers to start with 1. For analog subchannels the numbers can be defined with the new attribute R-x\AMCN-n-m. This means a subchannel declared as 1 in CH10 maps to the subchannel 1 in TMATS. For other data types a subchannel 0 in CH10 maps to 1 in TMATS.