C8051F50x-F51x
24.2. Data Format
UART0 has a number of available options for data formatting. Data transfers begin with a start bit (logic
low), followed by the data bits (sent LSB-first), a parity or extra bit (if selected), and end with one or two
stop bits (logic high). The data length is variable between 5 and 8 bits. A parity bit can be appended to the
data, and automatically generated and detected by hardware for even, odd, mark, or space parity. The stop
bit length is selectable between 1 and 2 bit times, and a multi-processor communication mode is available
for implementing networked UART buses. All of the data formatting options can be configured using the
SMOD0 register, shown in SFR Definition 24.2. Figure 24.2 shows the timing for a UART0 transaction
without parity or an extra bit enabled. Figure 24.3 shows the timing for a UART0 transaction with parity
enabled (PE0 = 1). Figure 24.4 is an example of a UART0 transaction when the extra bit is enabled
(XBE0 = 1). Note that the extra bit feature is not available when parity is enabled, and the second stop bit
is only an option for data lengths of 6, 7, or 8 bits.
MARK
START
BIT
STOP
BIT 1
STOP
BIT 2
D0
D1
DN-2
DN-1
SPACE
BIT TIMES
Optional
(6,7,8 bit
Data)
N bits; N = 5, 6, 7, or 8
Figure 24.2. UART0 Timing Without Parity or Extra Bit
MARK
SPACE
BIT TIMES
START
BIT
STOP
BIT 1
STOP
BIT 2
D0
D1
DN-2
DN-1
PARITY
Optional
(6,7,8 bit
Data)
N bits; N = 5, 6, 7, or 8
Figure 24.3. UART0 Timing With Parity
MARK
START
BIT
STOP
BIT 1
STOP
BIT 2
D0
D1
DN-2
DN-1
EXTRA
SPACE
BIT TIMES
Optional
(6,7,8 bit
Data)
N bits; N = 5, 6, 7, or 8
Figure 24.4. UART0 Timing With Extra Bit
Rev. 1.1
245
SILICON [ SILICON ]
