HD64F2357VF13 Datasheet, PDF (175/1049 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

RAS Down Mode and RAS Up Mode: Even when burst operation is selected, it may happen that access to DRAM space
is not continuous, but is interrupted by access to another space. In this case, if the RAS signal is held low during the
access to the other space, burst operation can be resumed when the same row address in DRAM space is accessed again.
• RAS down mode
To select RAS down mode, set the RCDM bit in MCR to 1. If access to DRAM space is interrupted and another space
is accessed, the RAS signal is held low during the access to the other space, and burst access is performed if the row
address of the next DRAM space access is the same as the row address of the previous DRAM space access. Figure 6-
21 shows an example of the timing in RAS down mode.
Note, however, that the RAS signal will go high if a refresh operation interrupts RAS down mode.
DRAM access
External space
access
DRAM access
T_p
T_r
T_c1
T_c2
T₁
T₂
T_c1
T_c2
ø
A₂₃ to A₀
CSn, (RAS)
CAS, LCAS
D₁₅ to D₀
Note: n = 2 to 5
Figure 6-21 Example of Operation Timing in RAS Down Mode
Rev.6.00 Oct.28.2004 page 145 of 1016
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