MC9S12HY64 Datasheet, PDF (450/792 Pages) Freescale Semiconductor, Inc – S12 Microcontrollers

Serial Communication Interface (S12SCIV5)
In Figure 12-24, 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 data samples RT8, RT9, and RT10 are within the bit time and data recovery is successful.
Perceived Start Bit
Actual Start Bit
LSB
RXD
Samples 1 1 1 0
0
1
0000
RT Clock
RT Clock Count
Reset RT Clock
Figure 12-24. Start Bit Search Example 3
Figure 12-25 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.
Perceived and Actual Start Bit
LSB
RXD
Samples 1 1 1 1 1 1 1 1 1 0
1
0
RT Clock
RT Clock Count
Reset RT Clock
Figure 12-25. Start Bit Search Example 4
MC9S12HY/HA-Family Reference Manual, Rev. 1.04
450
Freescale Semiconductor