h8s-2172 Renesas Electronics Corporation., h8s-2172 Datasheet - Page 338

• Manufacturer Part Number: h8s-2172
• Description: Renesas 16-bit Single-chip Microcomputer H8s Family H8s-2100 Series
• Manufacturer: Renesas Electronics Corporation.

11.4.2
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. Receive data is latched at the middle of each bit by sampling the data at
the rising edge of the 8th pulse of the basic clock as shown in figure 11.3. Thus the reception
margin in asynchronous mode is given by formula (1) below.
Where M: Reception Margin
Assuming values of F = 0 and D = 0.5 in formula (1), a reception margin is given by 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.
Rev. 2.00, 03/04, page 306 of 534
M = { (0.5 –
Internal base
clock
Receive data
(RxD)
Synchronization
sampling timing
Data sampling
timing
N: Ratio of bit rate to clock (N = 16)
D: Clock duty cycle (D = 0.5 to 1.0)
L: Frame length (L = 9 to 12)
F: Absolute value of clock rate deviation
Receive Data Sampling Timing and Reception Margin in Asynchronous Mode
Figure 11.3 Receive Data Sampling Timing in Asynchronous Mode
2N
1
) – (L – 0.5) F –
0
8 clocks
Start bit
16 clocks
7
D – 0.5
N
(1 + F) }
15 0
100 [%]
D0
7
... Formula (1)
15 0
D1