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13.4
Usage Notes
The following points should be noted when using the SCI as a smart card interface.
Receive Data Sampling Timing and Receive Margin in Smart Card Interface Mode: In smart
card interface mode, the SCI operates on a base clock with a frequency of 372 times the transfer
rate. In reception, the SCI synchronizes internally with the fall of the start bit, which it samples on
the base clock. Receive data is latched at the rising edge of the 186th base clock pulse. The timing
is shown in figure 13.11.
186 clocks
0
Internal base
clock
Receive data
(RxD)
Synchronization
sampling timing
Data sampling
timing
Figure 13.11 Receive Data Sampling Timing in Smart Card Interface Mode
372 clocks
185
371
0
Start bit
185
D0
371 0
D1
439
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