Dram Refresh Control - Renesas F-ZTAT H8 Series Hardware Manual

Section 7 Refresh Controller
7.3.2

DRAM Refresh Control

Refresh Request Interval and Refresh Cycle Execution: The refresh request interval is
determined by the settings of RTCOR and bits CKS2 to CKS0 in RTMCSR. Figure 7.2 illustrates
the refresh request interval.
RTCOR
H'00
Refresh request
Refresh requests are generated at regular intervals as shown in figure 7.2, but the refresh cycle is
not actually executed until the refresh controller gets the bus right.
Table 7.4 summarizes the relationship among area 3 settings, DRAM read/write cycles, and
refresh cycles.
Table 7.4 Area 3 Settings, DRAM Access Cycles, and Refresh Cycles
Area 3 Settings
2-state-access area
(AST3 = 0)
3-state-access area
(AST3 = 1)
To insert refresh cycles, set the RCYCE bit to 1 in RFSHCR. Figure 7.3 shows the state transitions
for execution of refresh cycles.
When the first refresh request occurs after exit from the reset state or standby mode, the refresh
controller does not execute a refresh cycle, but goes into the refresh request pending state. Note
this point when using a DRAM that requires a refresh cycle for initialization.
Rev. 7.00 Sep 21, 2005 page 170 of 878
REJ09B0259-0700
RTCNT
Figure 7.2 Refresh Request Interval (RCYCE = 1)
Read/Write Cycle by CPU
or DMAC
3 states
Wait states cannot be inserted
3 states
Wait states can be inserted
Refresh Cycle
3 states
Wait states cannot be inserted
3 states
Wait states can be inserted