When the receiver line “R” is pulled high on a RS-485 transceiver, a transition from transmitting to receiving can initiate a start condition in UART. When a half-duplex transceiver is switched from transmitting to receiving, the R line can experience a temporary voltage drop. The voltage drop on the R line can cause an unexpected start bit, generating a communication error. This application note explores the cause behind this false start condition and how to remove the false start.