25.3.2.2 Frame Formats

Data transfer is frame based, where a serial frame consists of one character of data bits with synchronization bits (Start and Stop bits) and an optional parity bit for error checking. This does not apply to master SPI operation (see 25.3.2.2.2 SPI Frame Formats.) The USART accepts all combinations of the following as valid frame formats:

  • 1 Start bit
  • 5, 6, 7, 8, or 9 Data bits
  • No, even, or odd Parity bit
  • 1 or 2 Stop bits

Figure 25-5 illustrates the possible combinations of frame formats. Bits inside brackets are optional.

Figure 25-5. Frame Formats
Table 25-4. Frame Format Nomenclature
Symbol Meaning
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