Levitron said:
(you can start from the line in 2nd gear)
There's the first evidence I've seen that Sportshift is in any way an actual improvement over a regular automatic transmission. In slippery winter driving conditions, sometimes starting off in 2nd makes the difference between going on your way and getting stuck.
Getting back to the original question, Sportshift is a conventional automatic transmission with electronic controls where the shifter has an extra "gate" with a toggle-style switch. The driver requests an upshift or downshift by pushing the lever momentarily one way or the other in the gate, which sends a signal to the tranny control module saying "up(down)shift requested." The controller then decides if an up- or downshift is permissible, then executes the shift.
The Sportshift tranny controller might be calibrated to execute faster, more abrupt shifts (i.e., trade "comfort" for a "performance" feel). However, that's just a different calibration of the same automatic transmission. You still don't have full command authority over the transmission (except for having the opportunity to bounce off of the rev limiter).
No flames intended to the Sportshift devotees. I just don't want one. I like my third pedal. 8)