HD6412332 RENESAS [Renesas Technology Corp], HD6412332 Datasheet - Page 207

• Manufacturer Part Number: HD6412332
• Description: Renesas 16-Bit Single-Chip Microcomputer H8S Family/H8S/2300 Series
• Manufacturer: RENESAS [Renesas Technology Corp]

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
Note: n = 2 to 5
A
CS
CAS, LCAS
D
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 when 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 occurs during RAS
down mode.
φ
23
15
n
to A
to D
(RAS)
0
0
Figure 6.21 Example of Operation Timing in RAS Down Mode
T
p
DRAM access
T
r
T
c1
T
c2
Rev.4.00 Sep. 07, 2007 Page 177 of 1210
space access
T
1
External
T
2
DRAM access
T
c1
REJ09B0245-0400
T
c2