SH7750_08 Datasheet, PDF (670/1162 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

Section 14 Direct Memory Access Controller (DMAC)
Operation: Figures 14.12 to 14.22 show the timing in each mode.
1. Cycle Steal Mode
In cycle steal mode, The DREQ sampling timing differs for dual address mode and single
address mode, and for level detection and edge detection of DREQ.
For example, in figure 14.12 (cycle steal mode, dual address mode, level detection), DMAC
transfer begins, at the earliest, four CKIO cycles after the first sampling operation. The second
sampling operation is performed one cycle after the start of the first DMAC transfer write
cycle. If DREQ is not detected at this time, sampling is executed in every subsequent cycle.
In figure 14.13 (cycle steal mode, dual address mode, edge detection), DMAC transfer begins,
at the earliest, five CKIO cycles after the first sampling operation. The second sampling
operation begins from the cycle in which the first DMAC transfer read cycle ends. If DREQ is
not detected at this time, sampling is executed in every subsequent cycle.
For details of the timing for various kinds of memory access, see section 13, Bus State
Controller (BSC).
Figure 14.18 shows the case of cycle steal mode, single address mode, and level detection. In
this case, too, transfer is started, at the earliest, four CKIO cycles after the first DREQ
sampling operation. The second sampling operation is performed one cycle after the start of
the first DMAC transfer bus cycle.
Figure 14.19 shows the case of cycle steal mode, single address mode, and edge detection. In
this case, transfer is started, at the earliest, five CKIO cycles after the first DREQ sampling
operation. The second sampling begins one cycle after the first assertion of DRAK.
In single address mode, the DACK signal is output every DMAC transfer cycle.
2. Burst Mode, Dual Address Mode, Level Detection
DREQ sampling timing in burst mode using dual address mode and level detection is virtually
the same as for cycle steal mode.
For example, in figure 14.14, DMAC transfer begins, at the earliest, four CKIO cycles after the
first sampling operation. The second sampling operation is performed one cycle after the start
of the first DMAC transfer write cycle.
In the case of dual address mode transfer initiated by an external request, the DACK signal can
be output in either the read cycle or the write cycle of the DMAC transfer according to the
specification of the AM bit in CHCR.
3. Burst Mode, Single Address Mode, Level Detection
DREQ sampling timing in burst mode using single address mode and level detection is shown
in figure 14.20.
Rev.7.00 Oct. 10, 2008 Page 586 of 1074
REJ09B0366-0700