Section 13 Serial Communication Interface (SCI)
Rev.2.00 Jun. 28, 2007 Page 483 of 666
REJ09B0311-0200
13.4.2
Receive Data Sampling Timing and Reception Margin in Asynchronous Mode
In asynchronous mode, the SCI operates on a basic clock with a frequency of 16 times the bit rate.
In reception, the SCI samples the falling edge of the start bit using the basic clock, and performs
internal synchronization. Since receive data is sampled at the rising edge of the 8th pulse of the
basic clock, data is latched at the middle of each bit, as shown in figure 13.3. Thus the reception
margin in asynchronous mode is determined by formula (1) below.
M = (0.5 – ) – (L – 0.5) F – (1
+
F ) | × 100 [%] ... Formula (1)
2N
1
N
| D – 0.5 |
M: Reception margin
N: Ratio of bit rate to clock (N = 16)
D: Duty cycle of clock (D = 0.5 to 1.0)
L: Frame length (L = 9 to 12)
F: Absolute value of clock frequency deviation
|
Assuming values of F = 0 and D = 0.5 in formula (1), the reception margin is determined by the
formula below.
M = ( 0.5 – ) × 100[%] = 46.875%
2 × 16
1
However, this is only the computed value, and a margin of 20% to 30% should be allowed in
system design.
Internal
basic clock
16 clocks
8 clocks
Receive data
(RxD)
Synchronization
sampling timing
Start bit
D0
D1
Data sampling
timing
15 0
7
15 0
0
7
Figure 13.3 Receive Data Sampling Timing in Asynchronous Mode
Содержание H8SX/1650
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Страница 106: ...Section 4 Exception Handling Rev 2 00 Jun 28 2007 Page 84 of 666 REJ09B0311 0200...
Страница 142: ...Section 5 Interrupt Controller Rev 2 00 Jun 28 2007 Page 120 of 666 REJ09B0311 0200...
Страница 326: ...Section 8 I O Ports Rev 2 00 Jun 28 2007 Page 304 of 666 REJ09B0311 0200...
Страница 470: ...Section 12 Watchdog Timer WDT Rev 2 00 Jun 28 2007 Page 448 of 666 REJ09B0311 0200...
Страница 546: ...Section 13 Serial Communication Interface SCI Rev 2 00 Jun 28 2007 Page 524 of 666 REJ09B0311 0200...
Страница 566: ...Section 14 A D Converter Rev 2 00 Jun 28 2007 Page 544 of 666 REJ09B0311 0200...
Страница 574: ...Section 16 RAM Rev 2 00 Jun 28 2007 Page 552 of 666 REJ09B0311 0200...
Страница 584: ...Section 17 Clock Pulse Generator Rev 2 00 Jun 28 2007 Page 562 of 666 REJ09B0311 0200...
Страница 638: ...Section 19 List of Registers Rev 2 00 Jun 28 2007 Page 616 of 666 REJ09B0311 0200...
Страница 668: ...Section 20 Electrical Characteristics Rev 2 00 Jun 28 2007 Page 646 of 666 REJ09B0311 0200...
Страница 676: ...Appendix Rev 2 00 Jun 28 2007 Page 654 of 666 REJ09B0311 0200...
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