HD6417750RF240V Datasheet, PDF (403/606 Pages) Renesas Technology Corp – Renesas 16-Bit Single-Chip Microcomputer H8S Family/H8S/2600 Series

Section 14 Serial Communication Interface (SCI)
14.7.4 Receive Data Sampling Timing and Reception Margin in Smart Card Interface
Mode
In Smart Card interface mode, the SCI operates on a basic clock with a frequency of 32, 64, 372,
or 256 times the transfer rate (fixed at 16 times in normal asynchronous mode) as determined by
bits BCP1 and BCP0. In reception, the SCI samples the falling edge of the start bit using the basic
clock, and performs internal synchronization. As shown in figure 14.25, by sampling receive data
at the rising-edge of the 16th, 32nd, 186th, or 128th pulse of the basic clock, data can be latched at
the middle of the bit. The reception margin is given by the following formula.
M = | (0.5 − ¹ ) − (L − 0.5) F − ^{| D − 0.5 |} (1 + F) | × 100%
2N
N
Where
M: Reception margin (%)
N: Ratio of bit rate to clock (N = 32, 64, 372, and 256)
D: Clock duty (D = 0 to 1.0)
L: Frame length (L = 10)
F: Absolute value of clock frequency deviation
Assuming values of F = 0, D = 0.5 and N = 372 in the above formula, the reception margin
formula is as follows.
M = (0.5 – 1/2 × 372) × 100%
= 49.866%
Rev. 7.00 Sep. 11, 2009 Page 367 of 566
REJ09B0211-0700