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MEMORY CONTROLLER
S3C2501X
5-52
5.7.9.3 Refresh Timer Register
The Refresh timer register is 32-bit read/write (some bits are read only) register. This register sets the SDRAM
refresh cycle. The refresh timer register is programmed with the number of system bus clock that should be
counted between SDRAM refresh cycles.
Table 5-27. SDRAM Refresh Timer Register
Registers
Address
R/W
Description
Reset value
REFREG
0xF0020008
R/W
Refresh timer register
0x00000020
REFREG
Bit
Description
R/W
Default value
REFCYC
[15:0]
SDRAM refresh cycle
R/W
0x00000020
[31:16]
Reserved
For example, for common refresh period of 15.6us, and a system bus clock frequency of 66MHz:
15.6 x 10
-6
x 66 x 10
6
= 1029
The refresh timer is set to 64 on reset. To ensure a refresh interval of less than 15.6us after reset, The minimum
frequency of system bus clock allowed is:
64 / (15.6 x 10
-6
)= 4.3 MHz
The refresh register should be written to as early as possible in the system start-up procedure, especially when
clock frequency is very low.
[15:0] SDRAM refresh cycle
[31:16] Reserved
0
15
RESERVED
REFCYC
Figure 5-25. SDRAM Refresh Timer Register
Содержание S3C2501X
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