MC68HC812A4 Datasheet, PDF (240/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Serial Communications Interface Module (SCI)
In Figure 14-7 the verification samples RT3 and RT5 determine that the
first low detected was noise and not the beginning of a start bit. The RT
clock is reset and the start bit search begins again. The noise flag is not
set because the noise occurred before the start bit was found.
In Figure 14-8 noise is perceived as the beginning of a start bit although
the verification sample at RT3 is high. The RT3 sample sets the noise
flag. Although the perceived bit time is misaligned, the data samples
RT8, RT9, and RT10 are within the bit time and data recovery is
successful.
START BIT
LSB
RXD
SAMPLES 1 1 1 0
1
110
0
0
0000
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 14-7. Start Bit Search Example 1
PERCEIVED START BIT
ACTUAL START BIT
LSB
RXD
SAMPLES 1 1 1 1 1 0
1
0
0000
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 14-8. Start Bit Search Example 2
MC68HC812A4 — Rev. 3.0
240
Serial Communications Interface Module (SCI)
Advance Information
MOTOROLA