1.4.1 UART TXDE Signal May Go Low before the STOP Bit Has Been Entirely Transmitted
The UART Transmit Drive Enable (TXDE) signal could potentially transition into a low state before the UART STOP bit has been entirely transmitted due to the effects of parasitic capacitance on the TX line. In some applications, this could result in communication being prematurely terminated due to the TXDE bit going low before the STOP bit has had enough time to settle.
Work around
To ensure that the STOP bit settles into its final logic state before the TXDE signal transitions low, a biasing circuit can be implemented. A biasing circuit allows the TX line to either be driven high or low, rather than being left in a floating tri-state mode where prolonged rise or fall times could lead to communication being disrupted. This bias circuit should only be implemented on one end of the serial bus, and a termination resistor should be used on the other end. The figure below shows an example of a bias circuit that can be used to achieve this.
Please note that the resistor values used in this circuit are recommendations and that the actual resistor values required may vary based on the application.
Affected Silicon Revisions
| B2 | C0 |
| X |