MSC8144E Reference Manual, Rev. 3
20-16
Freescale
Semiconductor
UART
In Figure 20-13, a large burst of noise is perceived as the beginning of a start bit, although the
test sample at RT5 is high. The RT5 sample sets the noise flag. Although this is a worst-case
misalignment of perceived bit time, the RT8, RT9, and RT10 data samples of the next bit are
within the bit time, and data recovery is successful.
Figure 20-14 shows the effect of noise early in the start bit time. Although this noise does not
affect proper synchronization with the start bit time, it does set the noise flag.
Figure 20-15 shows a burst of noise near the beginning of the start bit that causes the start bit not
to be found and resets the RT counter. 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.
Figure 20-13. Start Bit Search Example 4
Figure 20-14. Start Bit Search Example 5
Reset RT Counter
RT
1
RT
1
RT
1
RT
1
RT
2
RT
3
RT
4
RT
5
RT
6
RT
7
RT
8
RT
9
RT
1
0
RT
1
3
RT
1
2
RT
1
1
RT
1
6
RT
1
5
RT
1
4
RT
4
RT
3
RT
2
RT
1
RT
5
RT
6
RT
7
RT
8
RT
9
Samples
RT Clock
RT Clock Count
Actual Start Bit
URXD
1
0
1
1
1
0
0
0
0
LSB
0
Perceived Start Bit
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
2
RT
3
RT
4
RT
7
RT
6
RT
5
RT
1
0
RT
9
RT
8
RT
1
4
RT
1
3
RT
1
2
RT
1
1
RT
1
5
RT
1
6
RT
1
RT
2
RT
3
Perceived and Actual Start Bit
1
1
1
1
1
0
0
1
LSB
1
1
1
1
Reset RT Counter
Samples
RT Clock
RT Clock Count
URXD
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...