Section 9 Direct Memory Access Controller (DMAC)
Rev. 5.00 May 29, 2006 page 282 of 698
REJ09B0146-0500
Bus Modes: There are two bus modes: cycle-steal and burst. Select the mode in the TM bits of
CHCR_0 to CHCR_3 (one byte, word, or longword, or 16-byte data).
•
Cycle-Steal Mode
In the cycle-steal mode, the bus right is given to another bus master after a one-transfer-unit
(8-, 16-, or 32-bit unit) DMA transfer. When another transfer request occurs, the bus rights are
obtained from the other bus master and a transfer is performed for one transfer unit. When that
transfer ends, the bus right is passed to the other bus master. This is repeated until the transfer
end conditions are satisfied.
In the cycle-steal mode, transfer areas are not affected regardless of settings of the transfer
request source, transfer source, and transfer destination. Figure 9.14 shows an example of
DMA transfer timing in the cycle steal mode. Transfer conditions shown in the figure are:
Dual address mode
DREQ level detection
CPU
CPU
CPU
DMAC
DMAC
CPU
DMAC
DMAC
CPU
CPU
DREQ
Bus cycle
Bus right returned to CPU
Read
Write
Write
Read
Figure 9.14 DMA Transfer Example in the Cycle-Steal Mode
•
Burst Mode
In the burst mode, once the bus right is obtained, the transfer is performed continuously
without passing it until the transfer end conditions are satisfied. In the external request mode
with low level detection of the
DREQ
pin, however, when the
DREQ
pin is driven high, the
bus is passed to the other bus master after the DMAC transfer request that has already been
accepted ends, even if the transfer end conditions have not been satisfied.
The burst mode cannot be used when the serial communications interface (SCIF) and A/D
converter are the transfer request sources. Figure 9.15 shows a timing at this point.
CPU
CPU
CPU
DMAC
DMAC
DMAC
DMAC
DMAC
DMAC
CPU
DREQ
Bus cycle
Read
Read
Read
Write
Write
Write
Figure 9.15 DMA Transfer Example in the Burst Mode
Summary of Contents for SH7706 Series
Page 8: ...Rev 5 00 May 29 2006 page viii of xlviii ...
Page 160: ...Section 5 Cache Rev 5 00 May 29 2006 page 112 of 698 REJ09B0146 0500 ...
Page 370: ...Section 11 Watchdog Timer WDT Rev 5 00 May 29 2006 page 322 of 698 REJ09B0146 0500 ...
Page 554: ...Section 17 Pin Function Controller PFC Rev 5 00 May 29 2006 page 506 of 698 REJ09B0146 0500 ...
Page 576: ...Section 18 I O Ports Rev 5 00 May 29 2006 page 528 of 698 REJ09B0146 0500 ...
Page 746: ...Index Rev 5 00 May 29 2006 page 698 of 698 REJ09B0146 0500 ...
Page 749: ...SH7706 Group Hardware Manual ...