Samsung S3C2440A - Manual (Page 182)

S3C2440A RISC MICROPROCESSOR MEMORY CONTROLLER
DEC.13, 2002
5-17
REFRESH CONTROL REGISTER
Register Address R/W Description Reset Value
REFRESH 0x48000024 R/W SDRAM refresh control register 0xac0000
REFRESH Bit Description Initial State
REFEN [23] SDRAM Refresh Enable
0 = Disable 1 = Enable (self or CBR/auto refresh) 1
TREFMD [22] SDRAM Refresh Mode
0 = CBR/Auto Refresh 1 = Self Refresh
In self-refresh time, the SDRAM control signals are driven to the
appropriate level. 0
Trp [21:20] SDRAM RAS pre-charge Time
00 = 2 clocks 01 = 3 clocks 10 = 4 clocks 11 = Not support
10
Tsrc [19:18] SDRAM Semi Row cycle time
00 = 4 clocks 01 = 5 clocks 10 = 6 clocks 11 = 7 clocks
SDRAM Row cycle time: Trc=Tsrc+Trp
If Trp=3clocks & Tsrc=7clocks, Trc=3+7=10clocks.
11
Reserved [17:16] Not used 00
Reserved [15:11] Not used 0000
Refresh
Counter [10:0] SDRAM refresh count value. Refer to chapter 6 SDRAM refresh
controller bus priority section.
Refresh period = (2
11
-refresh_count+1)/HCLK
Ex) If refresh period is 7.8 us and HCLK is 100 MHz,
the refresh count is as follows:
Refresh count = 2
11
+ 1 - 100x7.8 = 1269
0