HD6417751RBP240V Datasheet, PDF (769/1226 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

15. Serial Communication Interface (SCI)
M: Receive margin (%)
N: Ratio of clock frequency to bit rate (N = 16)
D: Clock duty cycle (D = 0 to 1.0)
L: Frame length (L = 9 to 12)
F: Absolute deviation of clock frequency
From equation (1), if F = 0 and D = 0.5, the receive margin is 46.875%, as given by equation (2).
When D = 0.5 and F = 0:
M = (0.5 – 1/(2 × 16)) × 100% = 46.875% ............................................ (2)
This is a theoretical value. A reasonable margin to allow in system designs is 20% to 30%.
When Using the DMAC: When an external clock source is used as the serial clock, the transmit
clock should not be input until at least 5 peripheral operating clock cycles after SCTDR1 is
updated by the DMAC. Incorrect operation may result if the transmit clock is input within 4 cycles
after SCTDR1 is updated. (See figure 15.26)
SCK
t
TDRE
TxD
D0
D1
D2
D3
D4
D5
D6
D7
Note: When operating on an external clock, set t > 4.
Figure 15.26 Example of Synchronous Transmission by DMAC
When SCRDR1 is read by the DMAC, be sure to set the SCI receive-data-full interrupt (RXI) as
the activation source with bits RS3 to RS0 in CHCR.
When Using Synchronous External Clock Mode:
• Do not set TE or RE to 1 until at least 4 peripheral operating clock cycles after external clock
SCK has changed from 0 to 1.
• Only set both TE and RE to 1 when external clock SCK is 1.
Rev.4.00 Oct. 10, 2008 Page 669 of 1122
REJ09B0370-0400