25.3.2.1 Frame Formats

The USART data transfer is frame-based. A frame starts with a Start bit, followed by one character of data bits. If enabled, the Parity bit is inserted after the data bits and before the first Stop bit. After the Stop bit(s) of a frame, either the next frame can follow immediately, or the communication line can return to the Idle (high) state. The USART accepts all combinations of the following as valid frame formats:

• One Start bit
• Five, six, seven, eight, or nine data bits
• No, even, or odd Parity bit
• One or two Stop bits

The figure below illustrates the possible combinations of frame formats. Bits inside brackets are optional.

• St: Start bit, always low
• (n): Data bits (0 to 8)
• P: Parity bit, may be odd or even
• Sp: Stop bit, always high
• IDLE: No transfer on the communication line (RxD or TxD). The Idle state is always high.