UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
100 of 362
NXP Semiconductors
UM10208
Chapter 8: LPC2800 EMC
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
RFC
, or sometimes as t
RC
. This
register is accessed with one wait state.
shows the EMCDynamicTRFC Register.
10.15 Dynamic Memory Exit Self-refresh Register (EMCDynamictXSR -
0x8000 8050)
The EMCDynamicTXSR Register controls the exit-self-refresh-to-active-command time,
t
XSR
. 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
XSR
. This register is accessed with one wait state.
shows the EMCDynamicTXSR Register.
10.16 Dynamic Memory Active Bank A to Active Bank B Time Register
(EMCDynamictRRD - 0x8000 8054)
The EMCDynamicTRRD Register controls the active-bank-A-to-active-bank-B latency,
t
RRD
. 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
RRD
. This register is accessed with one wait state.
shows the EMCDynamictRRD Register.
Table 91.
Dynamic Memory Auto-refresh Period Register (EMCDynamictRFC - address
0x8000 804C)
Bit
Symbol
Description
POR Reset
Value
4:0
Auto-refresh
period and
auto-refresh to
active command
period (t
RFC
)
SDRAM initialization code should write this field with one
less than the number of AHB HCLK cycles that equals or
just exceeds the tRFC or tRC time specified for the
dynamic memory. The power-on reset value would select
32 AHB HCLK cycles.
0x1F
31:5
-
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit is not
defined.
-
Table 92.
Dynamic Memory Exit Self-refresh Register (EMCDynamictXSR - address
0x8000 8050)
Bit
Symbol
Description
POR Reset
Value
4:0
Exit self-refresh
to active
command time
(t
XSR
)
SDRAM initialization code should write this field with one
less than the number of AHB HCLK cycles that equals or
just exceeds the tXSR time specified for the dynamic
memory. The power-on reset value would select 32 AHB
HCLK cycles.
0x1F
31:5
-
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit is not
defined.
-