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VI SDRAM CONTROLLER BLOCK: SDRAM INTERFACE
S1C33L03 FUNCTION PART EPSON B-VI-2-17
A-1
B-VI
SDRAM
Refresh Mode
The SDRAM controller supports two SDRAM refresh modes: auto refresh and self-refresh.
Auto refresh
The SDRAM controller incorporates a 12-bit auto refresh counter. This counter continues counting on OSC3
clock edges, and when a specified count is reached, commands are sent to the SDRAM that precharges and
auto-refreshes all banks. The counter is reset at that time, and starts counting for the next refresh period. The
counter is also reset by self-refresh.
The auto-refresh period is determined by the OSC3 clock frequency and the count value set in the SDRARFC
[11:0] (D[B:0])/Auto refresh count register (0x39FFC6). For SDRARFC, set the appropriate value meeting
the specifications of your SDRAM. The count value is obtained by the equation below.
RFP
SDRARFC ≤ –––––––– × f
OSC3 - BL - CL - 2 × tRP - tRCD - 3
ROWS
RFP: Maximum refresh period [s]
ROWS: Row address size
f
OSC3:OSC3 clock frequency [Hz]
BL: Burst length [word]
CL: CAS latency [Number of SD_CLK cycles]
t
RP:PRECHARGE command period [Number of SD_CLK cycles]
t
RCD:ACTIVE to READ or WRITE delay time [Number of SD_CLK cycles]
If RFP = 64 ms, ROWS = 4,096, f
OSC3 = 20 MHz, BL = 8, CL = 3, tRP = 4, and tRCD = 4, for example, the
value to set is calculated as follows:
0.064
SDRARFC ≤ –––––––– × 20,000,000 - 8 - 3 - 2 × 4 - 4 - 3 = 286
4,096
Therefore, set any value equal to or less than 286 (0x11E) for SDRARFC.
BCLK
Command
SDCKE
#SDCEx
#SDRAS
#SDCAS
#SDWE
SDBA[1:0]
SDA[10]
SDA[12:11, 9:0]
LDQM/HDQM
DQ[15:0]
REF REFNOP
H
L
NOP NOPPALL NOP
t
RC
t
RP
Figure 2.15 Auto Refresh