15.5 Data format
A serial frame is defined to consist of one character of data bits with synchronization bits (start and
stop bits), and optionally a parity bit for error checking.
USART2 supports all 30 combinations of the followings as a valid frame format.
ï‚Ÿ 1 start bit
ï‚Ÿ 5, 6, 7, 8 or 9 data bits
ï‚Ÿ no, even or odd parity bit
ï‚Ÿ 1 or 2 stop bits
A frame starts with the start bit followed by the least significant data bit (LSB). The next data bits, up
to a total of nine, are succeeding, ending with the most significant bit (MSB). If enabled, the parity bit
is inserted after the data bits, before the stop bits. A high to low transition on data pin is considered as
start bit.
When a complete frame is transmitted, it can be directly followed by a new frame, or the
communication line can be set to an idle state. The idle means high state of data pin. The next figure
shows the possible combinations of the frame formats. Bits inside brackets are optional.
Figure 73. A Frame Format
Single data frame consists of the following bits
ï‚Ÿ Idle: No communication on communication line (TxD2/RxD2)
ï‚Ÿ St: Start bit (Low)
ï‚Ÿ Dn: Data bits (0~8)
ï‚Ÿ Parity bit: even parity, odd parity, no parity
ï‚Ÿ Stop bit(s): 1 bit or 2 bits
A frame format of the USARTn is set by USIZE[2:0], UPM[1:0] and USBS bits in UnCTRL1, UnCTRL3
register. The Transmitter and the Receiver use the same settings.
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