MOTOROLA
UNIVERSAL ASYNCHRONOUS RECEIVER/TRANSMITTER MODULE
MMC2001
11-22
REFERENCE MANUAL
Figure 11-15 Start Bit — Noise Case Three
Figure 11-15 illustrates the case where the start edge is qualified by the four logic
ones followed by a logic zero [1]. A burst of noise is present in the middle of the start
bit time. The noise [3] causes two out of the three data samples to be erroneously
detected as logic ones. This is rejected, therefore, as a start bit, because the majority
of samples RT8, RT9, and RT10 [3] suggest it should be a logic one.
RT
1
RT
1
RT
1
RT
1
RT
1
RT
1
RT
2
RT
4
RT
5
RT
6
RT
7
RT
8
RT
9
RT
3
RT
1
0
RT
1
1
RT
1
2
RT
1
3
RT
1
4
RT
1
5
RT
1
6
RT
1
RT
2
RT
3
RT
4
RT
5
RT
6
RT
7
1 1 1 1 1 0 0 0 0 0 0 0 0 1 1
RXD Pin
Samples
RT CLK
(16X Bit
Rate)
RT CLK
State
Reset RT
Actual Start Bit
No Start Bit Found
LSB
[1]
[2]
[3]
Freescale Semiconductor,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
nc.
..