In conventional, If there is no cam or VCO, its possible just to ramp the rpm based on measuring the AC track voltage. And for an OEM TMCC/command version where no cam or VCO was present, the railsounds software would omit the behavior I described earlier, where a cam pulse was required to confirm motion a few seconds after a relative speed command.
As you can imagine, there have been many small (and some large) variations on how this stuff works over time depending on the needs of a specific product or product class.
-Rudy
