Fujitsu FR60 Hardware Manual page 199

32-bit microcontroller mb91301 series
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[bit29 to bit24] RFINT5 to RFINT0 (ReFresh INTerval): Auto-refresh interval
Set these bits to the interval for automatic refreshing.
The auto-refresh interval can be obtained for distributed refresh mode {(REFINT5 to
REFINT0 value) x 32 x (external bus clock cycle)} or for centralized refresh mode {(REFINT5
to REFINT0 value) x 32 x (RFC specified number of times) x (external bus clock cycle)}
Calculate the design value in consideration of the maximum RAS active time.
To stop the auto refresh function, write "000000
The refresh counter keeps on being decremented even while the auto-refresh command is
being issued.
[bit23] BRST (BuRST refresh select): Burst refresh control
This bit is used to control the operation mode for auto-refreshing.
Table 4.2-44 shows the function of burst refresh control.
Table 4.2-44 Function of Burst Refresh Control
BRST
0
Distributed refresh (Auto-refresh is activated at intervals.)
1
Burst refresh (Auto-refresh is activated repeatedly at one time.)
When distributed refreshing is set, the auto-refresh command is issued once at every refresh
interval.
When burst refreshing is set, the auto-refresh command is issued continuously for the number
of times set in the refresh counter at every refresh interval.
[bit22 to bit20] RFC2, RFC1, RFC0 (ReFresh Count): Refresh count
Set these bits to the number of times a refresh must be performed to refresh all SDRAM.
Table 4.2-45 shows the number of times to refresh.
Table 4.2-45 Number of Times to Refresh
RFC2
RFC1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
The number of times to refresh specified here is the number of times centralized refreshing is
performed before and after transition to the self-refresh mode. When burst refreshing has been
selected with the BRST bit, the number of times to refresh is also the number of times the
refresh command is issued at every refresh interval.
CHAPTER 4 EXTERNAL BUS INTERFACE
" to the RFINT5 to REFINT0 bits.
B
Burst refresh control
RFC0
Number of times to refresh
0
1
0
1
0
1
0
1
256
512
1024
2048
4096
8192
Setting prohibited
Refresh prohibited
179

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