10 SDRAM CONTROLLER (SDRAMC)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
10-19
D24
SCKON: SDRAM Clock During Self-Refresh Bit
Specifies whether to stop the SDRAM clock during self-refresh or not.
1 (R/W): Enabled (output continued)
0 (R/W): Disabled (output disabled) (default)
Writing 0 to SCKON disables the SDRAM clock output from the SDCLK pin while the SDRAM is in
self-refresh mode. This helps to reduce the current consumption.
If SCKON is 1, the SDRAM clock is always output from the SDCLK pin even if the SDRAM is in self-
refresh mode.
D23
SELEN: SDRAM Self-Refresh Enable Bit
Enables the self-refresh control function of the SDRAM.
1 (R/W): Enabled
0 (R/W): Disabled (Default)
Writing 1 to SELEN enables the SDRAMC to start self-refreshing the SDRAM (by setting SDCKE
output low). Note that self-refreshing of the SDRAM actually begins a certain time after accessing or
auto-refreshing the SDRAM. The duration of this elapsed time is defined by the number of clock cycles
in SELCO[6:0].
To cancel self-refresh mode, perform the following procedure:
1. Disable self-refresh mode by clearing SELEN to 0.
2. Read data from an SDRAM address (any address can be specified).
3. Read SREFDO to check if self-refresh mode is canceled (SREFDO = 1).
D[22:16] SELCO[6:0]: SDRAM Self-Refresh Counter Bits
Sets the value for the self-refresh counter. (Default: 0x7f)
If SELEN is set to 1 (self-refresh enabled), the self-refresh counter starts counting up on the SDCLK
clock edges beginning with 0 after accessing or auto-refreshing the SDRAM. When the count specified
here is reached, the SDCKE output is pulled low, causing the SDRAM to start self-refreshing. If an ac-
cess to the SDRAM occurs during self-refresh, SDCKE returns high, thereby self-refresh mode is can-
celed.
D[15:12] Reserved
D[11:0] AURCO[11:0]: SDRAM Auto-Refresh Counter Bits
Sets the auto-refresh counter value. (Default: 0x8c)
The auto-refresh counter counts up on the SDCLK clock edges beginning with 0, and when the count
specified here is reached, the SDRAM controller sends an auto-refresh command. The counter is reset
at that point, and starts counting the next refresh period. The counter is also reset by self-refresh.
The value calculated from the equation below is the maximum count that can be set.
RFP
AURCO
≤
––––––––
×
f
CLK
- BL - CL - 2
×
t
RP
- t
RCD
- 3
ROWS
RFP:
Maximum refresh period [s]
ROWS: Row address size
f
CLK
:
SDCLK clock frequency [Hz]
BL:
Burst length (= 2)
CL:
CAS latency
t
RP
:
PRECHARGE command period [Number of cycles]
t
RCD
:
ACTIVE to READ/WRITE delay time [Number of cycles]