Rev. 1.00, 09/03, page 444 of 704
16.4.2
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. If 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 16.3. Thus the reception margin
in asynchronous mode is determined by formula (1) below.
M = (0.5 – ) – – (L – 0.5) F } × 100 [%] ... Formula (1)
2N
1
N
D – 0.5
M: Reception margin (%)
N : Ratio of bit rate to clock (N = 16)
D : Clock duty (D = 0.5 to 1.0)
L : Frame length (L = 9 to 12)
F : Absolute value of clock rate 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 – 1/(2 × 16)} × 100 [%] = 46.875 %
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 16.3 Receive Data Sampling Timing in Asynchronous Mode
Содержание H8S/2437
Страница 2: ...Rev 1 00 09 03 page ii of xxxviii ...
Страница 8: ...Rev 1 00 09 03 page viii of xxxviii ...
Страница 32: ...Rev 1 00 09 03 page xxxii of xxxviii ...
Страница 38: ...Rev 1 00 09 03 page xxxviii of xxxviii ...
Страница 168: ...Rev 1 00 09 03 page 130 of 704 ...
Страница 336: ...Rev 1 00 09 03 page 298 of 704 ...
Страница 402: ...Rev 1 00 09 03 page 364 of 704 ...
Страница 454: ...Rev 1 00 09 03 page 416 of 704 ...
Страница 512: ...Rev 1 00 09 03 page 474 of 704 ...
Страница 562: ...Rev 1 00 09 03 page 524 of 704 ...
Страница 648: ...Rev 1 00 09 03 page 610 of 704 ...
Страница 672: ...Rev 1 00 09 03 page 634 of 704 ...
Страница 732: ...Rev 1 00 09 03 page 694 of 704 ...
Страница 742: ...Rev 1 00 09 03 page 704 of 704 ...
Страница 745: ......
Страница 746: ...H8S 2437 Group Hardware Manual REJ09B0059 0100Z ...