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MC9S12VR-Family - Data Sheet - Freescale Semiconductor

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Serial Communication Interface (S12SCIV5)<br />

In Figure 10-24, a large burst of noise is perceived as the beginning of a start bit, although the test sample<br />

at RT5 is high. The RT5 sample sets the noise flag. Although this is a worst-case misalignment of perceived<br />

bit time, the data samples RT8, RT9, and RT10 are within the bit time and data recovery is successful.<br />

RXD<br />

Samples<br />

RT Clock<br />

RT Clock Count<br />

Reset RT Clock<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT2<br />

RT3<br />

RT4<br />

RT5<br />

RT6<br />

RT7<br />

RT8<br />

RT9<br />

Figure 10-24. Start Bit Search Example 3<br />

Figure 10-25 shows the effect of noise early in the start bit time. Although this noise does not affect proper<br />

synchronization with the start bit time, it does set the noise flag.<br />

RXD<br />

Samples<br />

RT Clock<br />

RT Clock Count<br />

Reset RT Clock<br />

Perceived Start Bit<br />

1 1 1 0 0 1 0 0 0 0<br />

Figure 10-25. Start Bit Search Example 4<br />

<strong>MC9S12VR</strong> <strong>Family</strong> Reference Manual, Rev. 2.8<br />

334 <strong>Freescale</strong> <strong>Semiconductor</strong><br />

RT10<br />

RT11<br />

1 1 1 1 1 1 1 1 1<br />

0 1 0<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT2<br />

RT3<br />

RT4<br />

RT5<br />

RT12<br />

RT6<br />

Actual Start Bit<br />

RT13<br />

RT7<br />

RT14<br />

RT8<br />

RT15<br />

RT9<br />

RT16<br />

RT10<br />

RT1<br />

Perceived and Actual Start Bit<br />

RT11<br />

RT2<br />

RT12<br />

RT3<br />

RT13<br />

RT4<br />

RT14<br />

RT5<br />

RT15<br />

RT6<br />

RT16<br />

RT7<br />

RT1<br />

LSB<br />

RT8<br />

LSB<br />

RT2<br />

RT9<br />

RT3

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