MC9S12C Datasheet, PDF (404/680 Pages) Motorola, Inc – 16-Bit Microcontroller

Chapter 13 Serial Communications Interface (S12SCIV2) Block Description
In Figure 13-16, 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
Rx input Signal
SAMPLES 1 1 1 0
0
1
0000
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 13-16. Start Bit Search Example 3
Figure 13-17 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
Rx Input Signal
SAMPLES 1 1 1 1 1 1 1 1 1 0
1
0
RT CLOCK
RT CLOCK COUNT
RESET RT CLOCK
Figure 13-17. Start Bit Search Example 4
404
MC9S12C-Family / MC9S12GC-Family
Freescale Semiconductor
Rev 01.23