Table 13.6 Idle Insertion Between Accesses - Hitachi SH7751 Hardware Manual

Table 13.6 Idle Insertion between Accesses

Read
Preceding
Cycle CPU DMA
Read
Write
DMA read


(memory
device)
DMA write D


(device
memory)
"DMA" in the table indicates DMA single-address transfer. DMA dual-address transfer is in
accordance with the CPU.
M, D : Idle wait always inserted by WCR1
(M(1): Once cycle inserted in MPX access even if WCR1 is cleared to 0)
M : Idle cycles according to setting of AnIW2-AnIW0 (areas 0 to 6)
D : Idle cycles according to setting of DMAIW2-DMAIW0
Notes: *1: Inserted when device is switched
*2: On the MPX interface, a WCR1 idle wait may be inserted before an access (either read
or write) to the same area after a write access. The specific conditions for idle wait
insertion in accesses to the same area are shown below.
(a) Synchronous DRAM set to RAS down mode
(b) Synchronous DRAM accessed by on-chip DMAC
Apart from use under above conditions (a) and (b), an idle wait is also inserted between
an MPX interface write access and a following access to the same area. Even under
the above conditions, an idle wait may be inserted in a same-area access following an
interface write access, depending on the synchronous DRAM pipeline access situation.
An idle wait is not inserted when the WCR1 register setting is 0. The setting for the
number of idle state cycles inserted after a power-on reset is the default value of 15 (the
maximum value), so ensure that the optimum value is set.
When synchronous DRAM is used in RAS down mode, set bits DMAIW2-DMAIW0 to
000 and bits A3IW2-A3IW0 to 000.
Same Area
Write
CPU DMA
M M
M M
1
D D D*
Following Cycle
Different Area
Read Write
CPU DMA CPU DMA
M M M
M M M
M M M
D D D
Rev. 3.0, 04/02, page 333 of 1064
Same Different
Area Area
MPX MPX
Address Address
Output Output
M M (1) M (1)
2
M * M
M — M (1)
D — D (1)