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UM10503
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User manual
Rev. 1.3 — 6 July 2012
481 of 1269
NXP Semiconductors
UM10503
Chapter 21: LPC43xx External Memory Controller (EMC)
21.7.14 Dynamic Memory Auto-refresh Period register
The DYNAMICTRFC register enables you to program the auto-refresh period, and
auto-refresh to active command period, tRFC. It is recommended that this register is
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
tRFC, or sometimes as tRC. This register is accessed with one wait state.
Note: This register is used for all four dynamic memory chip selects. Therefore the worst
case value for all of the chip selects must be programmed.
21.7.15 Dynamic Memory Exit Self Refresh register
The DYNAMICTXSR register enables you to program the exit self-refresh to active
command time, tXSR. It is recommended that this register is 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 tXSR. This register is accessed
with one wait state.
Note: This register is used for all four dynamic memory chip selects. Therefore the worst
case value for all of the chip selects must be programmed.
21.7.16 Dynamic Memory Active Bank A to Active Bank B Time register
The DYNAMICTRRD register enables you to program the active bank A to active bank B
latency, tRRD. It is recommended that this register is 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 tRRD. This register is accessed with one wait
state.
Table 367. Dynamic Memory Auto Refresh Period register (DYNAMICRFC - address
0x4000 504C) bit description
Bit
Symbol
Description
Reset
value
4:0
TRFC
Auto-refresh period and auto-refresh to active command period.
0x0 - 0x1E = n + 1 clock cycles. The delay is in CCLK cycles.
0x1F = 32 clock cycles (POR reset value).
0x1F
31:5
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-
Table 368. Dynamic Memory Exit Self Refresh register (DYNAMICXSR - address
0x4000 5050) bit description
Bit
Symbol
Description
Reset
value
4:0
TXSR
Exit self-refresh to active command time.
0x0 - 0x1E = n + 1 clock cycles. The delay is in CCLK cycles.
0x1F = 32 clock cycles (POR reset value).
0x1F
31:5
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-