Renesas SH7641 - Manual (Page 796)

Section 19 Serial Communication Interface with FIFO (SCIF)
Rev. 4.00 Sep. 14, 2005 Page 746 of 982
REJ09B0023-0400
6. When Using the DMAC
 Using an External Clock in Chock Synchronous Mode:
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 cycles. A
malfunction may occur when the transfer clock is input within four cycles after updating
SCFTDR (figure 19.20).
SCK
TDRE
TxD D0 D1 D2 D6 D7 D3 D4 D5
t
Note: When the SCIF is operated on an external clock, set t > 4.
Figure 19.20 DMA Transfer Example in the Synchronization Clock
 DMA Transfer Request:
When a DMA transfer is requested from the SCIF of which transfer request is allowed by
the DMAC, the transfer request from the SCIF is held in the DMAC. This transfer request
is cleared after it is actually transferred.
Even if the DME bit of the DMA operation register (DMAOR) and the DE bit of the DMA
channel control register (CHCR) are cleared, the DMA transfer request from the SCIF is
retained. In this state, note that the DMA transfer is done for one time without any DMA
transfer request from the SCIF when the DMAC allows the transfer request from the SCIF.
 TEND Flag:
When the transmit FIFO data empty DMA transfer request is generated and the transmit
data is written to SCFTDR by the DMAC, the value indicated by the TEND flag is
undefined. Thus, do not use the TEND flag as a transmit end flag.