I have been looking at the user manuals for the Ft 857, Ft 450, and the Ft 950. They all say they support the FC-40 auto coupler. The Ft 857 and the Ft 450 say they also support the FC-30. However, Yaesu seems to have a typo in their manual in that they have reversed the TX D and RX D pins in the CAT jack diagram (schematic). I cannot believe that they really would have reversed these as that would eliminate compatibility with their older antenna couplers. Further, the pin 6 on the 857 is listed as "Band Data" while on the 950 and the 450 it is listed as "TUNER SENSE".
Question one is, are the pins actually reversed, or is this a typo?
Question two is, is Band Data and Tuner Sense, one and the same?
It appears (at least with the FC40), that they either tie the pin up or down, so the radio knows there is a tuner attached.
Question three is, does any one know whether it is tied high (Vcc) or low (chassis ground)?