HD64F38024HV Datasheet, PDF (404/684 Pages) Renesas Technology Corp – Hardware Manual Renesas 8-Bit Single-Chip Microcomputer H8 Family/H8/300L Super Low Power Series

Section 10 Serial Communication Interface
Internal
basic clock
Receive data
(RXD32)
Synchronization
sampling timing
16 clock pulses
8 clock pulses
0
7
Start bit
15 0
7
D0
15 0
D1
Data sampling
timing
Figure 10.16 Receive Data Sampling Timing in Asynchronous Mode
Consequently, the receive margin in asynchronous mode can be expressed as shown in equation
(1).
M ={(0.5 – ¹ ) – ^{D – 0.5} – (L – 0.5) F} × 100 [%] ..... Equation (1)
2N
N
where
M: Receive 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 frequency deviation
Substituting 0 for F (absolute value of clock frequency deviation) and 0.5 for D (clock duty) in
equation (1), a receive margin of 46.875% is given by equation (2).
When D = 0.5 and F = 0,
M = {0.5 – 1/(2 × 16)} × 100 [%]
= 46.875%
.... Equation (2)
However, this is only a computed value, and a margin of 20% to 30% should be allowed when
carrying out system design.
Rev. 8.00 Mar. 09, 2010 Page 382 of 658
REJ09B0042-0800