The RXD output structure is an open-drain output stage. This allows the TLIN1029-Q1 to be used with 3.3- V and 5-V I/O processor. If the RXD pin of the processor does not have an integrated pull-up, an external pull-up resistor to the processor I/O supply voltage is required. The select external pull-up resistor value should be between 1 kΩ to 10 kΩ, depending on supply used (See I_OL in electrical characteristics). The V_SUP pin of the device should be decoupled with a 100-nF capacitor as close to the supply pin of the device as possible.