46.7.9.8.6 Indeterminate Time
See comm_type.
Like Beta1, the IDT value is different depending on whether the previous frame was transmitted or received.
IDTRx and IDTTx can be configured respectively through the USART LON IDT Rx register (FLEX_US_LONIDTRX) and the USART LON IDT Tx register (FLEX_US_LONIDTTX).