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II CORE BLOCK: BCU (Bus Control Unit)
S1C33210 FUNCTION PART EPSON B-II-4-29
Operation in successive RAS mode
Example: RAS: 2 cycles; CAS: 1 cycle; Precharge: 2 cycles
BCLK
A[11:0]
#RASx
#HCAS/
#LCAS
#DRD
#DWE
RAS
cycle
Accsess to other
device than DRAM
Not asserted for areas
other than DRAM
Precharge
cycle
Deassert
cycle
Assert
cycle
CAS cycles
in page mode
RAS
cycle
CAS
cycles
CAS cycles
in page mode
(1) (2) (3) (4)
Figure 4.35 Operation in Successive RAS Mode
(1) When accessing the DRAM area, an ordinary RAS cycle is executed first.
(2) If access to the same DRAM is suspended during a page mode, #RASx remains asserted while some other
device is accessed. In this case, a cycle to temporarily deassert #DRD/#DWE is inserted before accessing the
other device.
(3) If access to the same page in the same DRAM area as in (1) is requested after (2), #DRD/#DWE is asserted
back again to restart the page mode.
(4) A precharge cycle is executed when one of the following conditions that cause the page mode to suspend is
encountered:
• access to different DRAM is requested;
• access to a different page in the same DRAM area is requested;
• access to some other device than DRAM is requested;
• CAS-before-RAS refresh is requested; and
• relinquishing of bus control is requested by an external bus master.
Note: When using the successive RAS mode, always be sure to use #DRD for the read signal and #DWE
for the low-byte write signal.