UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
97 of 362
NXP Semiconductors
UM10208
Chapter 8: LPC2800 EMC
10.8 Dynamic Memory Active to Precharge Command Period Register
(EMCDynamictRAS - 0x8000 8034)
The EMCDynamicTRAS Register controls the active-to-precharge command period, t
RAS
.
This register should only be modified during system initialization, or when there are no
current or outstanding transactions. This can be ensured by waiting until the EMC is idle,
and then entering low-power or disabled mode. This value is normally found in SDRAM
data sheets as t
RAS
. This register is accessed with one wait state.
shows the EMCDynamicTRAS Register.
10.9 Dynamic Memory Self-refresh Exit Time Register
(EMCDynamictSREX - 0x8000 8038)
The EMCDynamicTSREX Register controls the self-refresh exit time, t
SREX
. This register
should only be modified during system initialization, or when there are no current or
outstanding transactions. This can be ensured by waiting until the EMC is idle, and then
entering low-power or disabled mode. This value is normally found in SDRAM data sheets
as t
SREX
. For devices without this parameter use the value of tXSR. This register is
accessed with one wait state.
shows the EMCDynamictSREX Register.
Table 85.
Dynamic Memory Active to Precharge Command Period Register
(EMCDynamictRAS - address 0x8000 8034)
Bit
Symbol
Description
POR
Reset
Value
3:0
Active-to-
precharge
command
period (t
RAS
)
SDRAM initialization code should write this field with one less
than the number of AHB HCLK cycles that equals or just
exceeds the tRAS time specified for the dynamic memory. The
power-on reset value would select 16 AHB HCLK cycles.
0xF
31:4
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
-
Table 86.
Dynamic Memory Self-refresh Exit Time Register (EMCDynamictSREX - address
0x8000 8038)
Bit
Symbol
Description
POR
Reset
Value
3:0
Self-refresh exit
time (t
SREX
)
SDRAM initialization code should write this field with one less
than the number of AHB HCLK cycles that equals or just
exceeds the tSREX or tXSR time specified for the dynamic
memory. The power-on reset value would select 16 AHB HCLK
cycles.
0xF
31:4
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
-