Automatic transmissions control systems have a key influence on the overall powertrain performance.These systems are coruplex to test and validate due to the interaction of mechanics,hydraulics,ele.ctronics.vehicle dynamics,drive.r inputs and transmission control software.It is necessary to balance gearshift timing,passenger comfort,clutch temperature etc….In this context.realistic and accurate dynamic plant models,capable of real-time simulation,are very valuable tools.In this paper,we describe how the plant models for a new 6AT gearbox with start/stop function were developed,using a physical modeling language,Modelica.The model includes driver,engine,EMS with start/stop function,torque converter,planetary gears,hydraulic control modules with solenoid valves,thermal computations and oil cooler.driveline,tyres,longitudinal vehicle dynamics,1/0 and CAN signals management.A special focus is done on real-time capahility and model requirements for interfacing and testing the TCU with a dSPACE SCALEXIO system.Finally,the model is validated by comparison with early measurements obtained from a gearbox prototype on its test bench.