Section 21 Serial Communication Interface with FIFO (SCIF)
Rev.1.00 Dec. 13, 2005 Page 796 of 1286
REJ09B0158-0100
Thus, the reception margin in asynchronous mode is given by formula (1).
1
| D - 0.5 |
M= (0.5
-
2N
) - (L - 0.5) F -
N
(1 + F)
×
100 % .................. (1)
M: Receive
margin
(%)
N: Ratio of bit rate to clock (N = 16)
D: Clock duty (D = 0 to 1.0)
L: Frame length (L = 9 to 12)
F:
Absolute value of clock rate deviation
From equation (1), if F = 0 and D = 0.5, the reception margin is 46.875%, as given by formula (2).
When D = 0.5 and F = 0:
M = (0.5 – 1 / (2
×
16) )
×
100% = 46.875% ............................................... (2)
However, this is a theoretical value. A reasonable margin to allow in system designs is 20% to
30%.
(6) When Using DMAC to Update SCFTDR in External Clock Synchronizing
When using an external clock as the synchronization clock, after SCFTDR is updated by the
DMAC, an external clock should be input after at least five peripheral clock (Pck) cycles. A
malfunction may occur when the transfer clock is input within four cycles after updating SCFTDR
(see figure 21.23).
SCIF_SCK
TDFE flag
SCIF_TXD
Note: When the SCIF is operated on an external clock, set t to ensure 5 Pck clock cycles or more.
D0
D1
D2
D6
D7
D3
D4
D5
t
Figure 21.23 Example of Synchronization Clock Transfer by DMAC
Содержание SH7780 Series
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