353
8331B–AVR–03/12
Atmel AVR XMEGA AU
27.11.2
CTRLB (SRAM) – Control register B
The configuration options for this register depend on the chip select mode configuration. The
register description below is valid when the chip select mode is configured for SRAM or SRAM
LPC.
• Bit 7:3 – Reserved
These bits are unused and reserved for future use.
• Bit 2:0 – SRWS[2:0]: SRAM Wait State
These bits select the number of wait states for SRAM and SRAM LPC access as a number of
Clk
PER2
cycles, according to
.
27.11.3
CTRLB (SDRAM) – Control register B
The configuration options for this register depend on the chip select mode configuration. The
register description below is valid for CS3 when the chip select mode is configured for SDRAM
.
• Bit 7 – SDINITDONE: SDRAM Initialization Complete
This flag is set at the end of the SDRAM initialization sequence. The flag will remain set as long
as the EBI is enabled and the Chip Select is configured for SDRAM.
• Bit 6:3 – Reserved
These bits are unused and reserved for future use.
• Bit 2 – SDSREN: SDRAM Self-refresh Enable
When this bit is written to one the EBI controller will send a Self-refresh command to the
SDRAM. For leaving the self refresh mode, the bit must be written to zero.
Bit
7
6
5
4
3
2
1
0
+0x01
–
–
–
–
–
SRWS[2:0]
CTRLB
Read/Write
R
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Table 27-23.
Wait State selection
SRWS[2:0]
Group Configuration
Description
000
0CLK
Zero Clk
PER2
cycles wait state
001
1CLK
One Clk
PER2
cycles wait state
010
2CLK
Two Clk
PER2
cycles wait state
011
3CLK
Three Clk
PER2
cycles wait state
100
4CLK
Four Clk
PER2
cycles wait state
101
5CLK
Five Clk
PER2
cycles wait state
110
6CLK
Six Clk
PER2
cycles wait state
111
7CLK
Seven Clk
PER2
cycles wait state
Bit
7
6
5
4
3
2
1
0
+0x01
SDINITDONE
–
–
–
–
SDREN
SDMODE[1:0]
CTRLB
Read/Write
R/W
R
R
R
R
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0