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MC9S12VR-Family - Data Sheet - Freescale Semiconductor

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

Serial Communication Interface (S12SCIV5)<br />

In Figure 10-22 the verification samples RT3 and RT5 determine that the first low detected was noise and<br />

not the beginning of a start bit. The RT clock is reset and the start bit search begins again. The noise flag<br />

is not set because the noise occurred before the start bit was found.<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 />

RT1<br />

RT1<br />

RT2<br />

RT3<br />

Figure 10-22. Start Bit Search Example 1<br />

In Figure 10-23, verification sample at RT3 is high. The RT3 sample sets the noise flag. Although the<br />

perceived bit time is misaligned, the data samples RT8, RT9, and RT10 are within the bit time and data<br />

recovery is successful.<br />

RXD<br />

Samples<br />

RT Clock<br />

RT Clock Count<br />

Reset RT Clock<br />

Figure 10-23. Start Bit Search Example 2<br />

<strong>Freescale</strong> <strong>Semiconductor</strong> 333<br />

RT4<br />

RT5<br />

RT6<br />

Start Bit<br />

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

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT1<br />

RT2<br />

RT3<br />

RT4<br />

RT5<br />

RT6<br />

RT7<br />

Perceived Start Bit<br />

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

RT7<br />

RT8<br />

RT9<br />

RT10<br />

RT11<br />

RT8<br />

RT9<br />

Actual Start Bit<br />

RT12<br />

RT13<br />

RT10<br />

RT14<br />

RT11<br />

RT15<br />

RT12<br />

RT16<br />

RT13<br />

RT1<br />

RT14<br />

RT2<br />

RT15<br />

RT3<br />

RT16<br />

RT4<br />

RT1<br />

RT5<br />

LSB<br />

RT2<br />

LSB<br />

RT6<br />

RT3<br />

RT7

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