Section 15 Serial Communication Interface (SCI)
Rev. 1.00 Apr. 28, 2008 Page 452 of 994
REJ09B0452-0100
15.7.4
Receive Data Sampling Timing and Reception Margin
Only the internal clock generated by the internal baud rate generator can be used as a
communication clock in smart card interface mode. In this mode, the SCI can operate using a
basic clock with a frequency of 32, 64, 372, or 256 times the bit rate according to the BCP1 and
BCP0 settings (the frequency is always 16 times the bit rate in normal asynchronous mode). At
reception, the falling edge of the start bit is sampled using the internal basic clock in order to
perform internal synchronization. Receive data is sampled at the 16th, 32nd, 186th and 128th
rising edges of the basic clock pulses so that it can be latched at the center of each bit as shown in
figure 15.25. The reception margin here is determined by the following formula.
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 = 32, 64, 372, 256)
D: Clock duty (D = 0 to 1.0)
L: Frame length (L = 10)
F: Absolute value of clock rate deviation
Assuming values of F = 0, D = 0.5, and N = 372 in formula (1), the reception margin is
determined by the formula below.
M = (0.5 – 1 / 2
×
372)
×
100 [%] = 49.866%
Internal
basic clock
372 clock cycles
186 clock
cycles
Receive data
(RxD)
Synchronization
sampling timing
D0
D1
Data sampling
timing
185
371 0
371
185
0
0
Start bit
Figure 15.25 Receive Data Sampling Timing in Smart Card Interface Mode
(When Clock Frequency is 372 Times the Bit Rate)
Содержание H8S/2100 Series
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Страница 416: ...Section 13 8 Bit Timer TMR Rev 1 00 Apr 28 2008 Page 390 of 994 REJ09B0452 0100...
Страница 494: ...Section 15 Serial Communication Interface SCI Rev 1 00 Apr 28 2008 Page 468 of 994 REJ09B0452 0100...
Страница 612: ...Section 18 I 2 C Bus Interface IIC Rev 1 00 Apr 28 2008 Page 586 of 994 REJ09B0452 0100...
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