Start Bit - Noise Case Three - Motorola M-CORE MMC2001 Series Reference Manual

RXD Pin
Samples
1 1 1 1 1
[1]
RT CLK
(16X Bit
Rate)
RT CLK
State
Reset RT
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.
MOTOROLA UNIVERSAL ASYNCHRONOUS RECEIVER/TRANSMITTER MODULE
11-22
Freescale Semiconductor, Inc.
No Start Bit Found
Actual Start Bit
0 0 0 0 0 0 0 0
[2]
Figure 11-15 Start Bit — Noise Case Three
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1 1
[3]
LSB
MMC2001
REFERENCE MANUAL