starting the ADC by hardware signal

Hi, in the 335x manual I can see that there is a way to start the ADC by hardware signal:

12.3.1 HW Synchronized or SW Channels
The user can control the start behavior of each channel input by deciding if a channel should be sampled
immediately (SW enabled) after it is enabled, or if the channel should wait for a HW event to occur first ( a
HW event must either be mapped to the touch screen PEN event or mapped to the HW event input signal…

does anyone know how can i use it (is it pinedout)?