642
/
838
Nations Technologies Inc.
Tel
：
+86-755-86309900
：
Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
an interruption occurs and will not Set the NEF noise flag.
The samples of the 3rd, 5th, and 7th bits have two '0' points, and at the same time, the samples of the 8th, 9th, and
10th bits have three '0' points, then the start bit is confirmed, but it will be set NEF noise flag.
The samples of the 3rd, 5th, and 7th bits have three '0' points, and at the same time, the samples of the 8th, 9th, and
10th bits have two '0' points, then the start bit is confirmed, but it will be set NEF noise flag.
The samples of the 3rd, 5th, and 7th bits have two '0' points, and at the same time, the samples of the 8th, 9th, and
10th bits have two '0' points, then it is confirmed that the start bit is received, but it will be set bit NEF noise flag.
If the sampling values in the 3rd, 5th, 7th, 8th, 9th and 10th bits cannot meet the above four requirements, the USART
receiver thinks that it has not received the correct start bit, and will exit the start bit detection and Return to idle state
and wait for falling edge.
Figure 23-6 Start bit detection
Stop bit description
During data reception, the number of data stop bits can be configured by the USART_CTRL2.STPB[1:0]. In normal
mode, 1 or 2 stop bits can be selected. In Smartcard mode, 0.5 or 1.5 stop bits can be selected.
1.
0.5 stop bits (receive in smartcard mode): 0.5 stop bits are not sampled. Therefore, if 0.5 stop bits is selected,
framing errors and broken frames cannot be detected.
2.
1 stop bit: the sampling of one stop bit is carried out through three points, and the 8th, 9th and 10th sampling
bits are selected.
3.
1.5 stop bit (Smartcard mode): when sending in Smartcard mode, the device must check whether the data is sent
correctly. So the receiver function block must be activated (USART_CTRL1.RXEN=1) and sample the signal
RX line
sample
clock
Conditions
to validate
the start bit
Falling edge
detection
At least 2 bits
out of 3 at 0
At least 2 bits
out of 3 at 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
One-bit time
1
1
1
0
x
0
x
0
x
0
0
0
0
x
x
x
x
x
x
