K60P100M100SF2RM Datasheet, PDF (1535/1809 Pages) Freescale Semiconductor, Inc – K60 Sub-Family Reference Manual

Chapter 51 Universal Asynchronous Receiver/Transmitter (UART)
PERCEIVED START BIT
Rx pin input
ACTUAL START BIT
LSB
SAMPLES 1 1 1 0
0
1
0000
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 51-193. 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.
PERCEIVED AND ACTUAL START BIT
LSB
Rx pin input
SAMPLES 1 1 1 1 1 1 1 1 1 0
1
0
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 51-194. 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.
K60 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc.
1535