NXP Semiconductors K22F series, Reference Manual, Page: 1271 / 1407

SAMPLES
Rx pin input
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
1 1 1 0 0 1 0 0 0 0
PERCEIVED START BIT
ACTUAL START BIT LSB
R
T1
R
T1
R
T1
R
T1
R
T2
R
T4
R
T3
R
T5
R
T6
R
T7
R
T8
R
T9
R
T1
0
R
T1
1
R
T1
5
R
T1
4
R
T1
3
R
T1
2
R
T1
6
R
T1
R
T2
R
T3
R
T4
R
T5
R
T6
R
T7
R
T8
R
T9
Figure 47-7. Start bit search example 3 (C7816[ISO_7816E] = 0)
The following figure shows the effect of noise early in the start bit time. In this example
C7816[ISO_7816E] = 0. Although this noise does not affect proper synchronization with
the start bit time, it does set the noise flag.
SAMPLES
Rx pin input
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
1 1 1 1 0
PERCEIVED AND ACTUAL START BIT LSB
R
T1
R
T1
R
T1
R
T1
R
T1
R
T1
R
T1
R
T1
R
T1
R
T1
R
T2
R
T3
R
T4
R
T5
R
T1
R
T2
R
T3
R
T6
R
T7
R
T8
R
T9
R
T1
0
R
T1
1
R
T1
2
R
T1
3
R
T1
4
R
T1
5
R
T1
6
1 1 1 1 1 1 0
Figure 47-8. Start bit search example 4 (C7816[ISO_7816E] = 0)
The following figure shows a burst of noise near the beginning of the start bit that resets
the RT clock. In this example C7816[ISO_7816E] = 0. The sample after the reset is low
but is not preceded by three high samples that would qualify as a falling edge. Depending
on the timing of the start bit search and on the data, the frame may be missed entirely or it
may set the framing error flag.
Chapter 47 Universal Asynchronous Receiver/Transmitter (UART)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 1271