
M0A21/M0A23 Series
May 06, 2022
Page
499
of 746
Rev 1.02
M0
A21
/M
0
A
2
3
SE
RIES
TEC
H
NICAL
RE
FEREN
C
E
M
ANUAL
USCIx_DAT1
X
Table 6.13-1 Input Signals for UART Protocol
Output Signals
For UART protocol, up to each protocol-related output signals are available. The number of actually
used outputs depends on the selected protocol. They can be classified according to their meaning for
the protocols.
Selected Protocol
UART
Control Output
USCIx_CTL0
X
USCIx_CTL1
nRTS
Data Output
USCIx_DAT0
X
USCIx_DAT1
TX
Table 6.13-2 Output Signals for Different Protocol
Frame Format
A standard UART frame is shown in Figure 6.13-3. It consists of:
An idle time with the signal level 1.
One start of frame bit (SOF) with the signal level 0.
6~13 bit data
A parity bit (P), programmable for either even or odd parity. It is optionally possible to
handle frames without parity bit.
One or two stop bits with the signal level 1.
IDLE
SOF
1
0
1 Bit
6~13 Bit
DATA
P
STOP
IDLE
1~2 Bit
0~1 Bit
Figure 6.13-3 UART Standard Frame Format
The protocol specific bits (SOF, P, STOP) are automatically handled by the UART protocol state
machine and do not appear in the data flow via the receive and transmit buffers.
Start Bit
The receiver input signal USCIx_DAT0 is checked for a falling edge. An SOF bit is detected when a
falling edge occurs while the receiver is idle or after the sampling point of the last stop bit. To increase
noise immunity, the SOF bit timing starts with the first falling edge that is detected. If the sampled bit
value of the SOF is 1, the previous falling edge is considered to be due to noise and the receiver is
considered to be idle again.
Data Field
The length of the data field (number of data bits) can be programmed by the bit field of DWIDTH
(UUART_LINECTL[11:8]). It can vary between 6 to 13 data bits.
Note:
In UART protocol, the data transmission order is LSB first by setting LSB (UUART_LINECTL[0])
to 1.
Parity Bit