Thanks so much JuroV, I was using Codewarrior 6.3, USB stack 3.1.1
CDC demo for 51JE256 and this was exactly what I needed to do to get my demo working.
In the virtual_com.c file (near the bottom of the page) is the
static void USB_Notify_Callback ( uint_8 controller_ID, /* [IN] Controller ID */ uint_8 event_type, /* [IN] PSTN Event Type */ void* val /* [IN] gives the configuration value */){ UNUSED (controller_ID) UNUSED (val) if(start_app == TRUE) { start_transactions = TRUE; if(event_type == USB_APP_CDC_CARRIER_ACTIVATED) { // start_transactions = TRUE; } else if(event_type == USB_APP_CDC_CARRIER_DEACTIVATED) { // start_transactions = FALSE; } } return;}