UM10503
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User manual
Rev. 2.1 — 10 December 2015
606 of 1441
NXP Semiconductors
UM10503
Chapter 23: LPC43xx/LPC43Sxx External Memory Controller (EMC)
23.7.7 Dynamic Memory Precharge Command Period register
This register enables you to program the precharge command period, tRP. This register
must only be modified during system initialization. This value is normally found in SDRAM
data sheets as tRP. 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.
23.7.8 Dynamic Memory Active to Precharge Command Period register
This register enables you to program the active to precharge command period, tRAS. 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 tRAS. 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.
Table 420. Dynamic Memory Read Configuration register (DYNAMICREADCONFIG, address
0x4000 5028) bit description
Bit
Symbol
Value Description
Reset
value
1:0
RD
Read data strategy.
0x0
0x0
Do not use. POR reset value.
0x1
Command delayed by 1/2 EMC_CCLK.
0x2
Command delayed by 1/2 EMC_CCLK plus one clock cycle.
0x3
Command delayed by1/2 EMC_CCLK plus two clock cycles,
31:2
-
-
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
-
Table 421. Dynamic Memory Precharge Command Period register (DYNAMICRP, address
0x4000 5030) bit description
Bit
Symbol
Description
Reset
value
3:0
TRP
Precharge command period.
0x0 - 0xE = n + 1 clock cycles. The delay is in EMC_CCLK cycles.
0xF = 16 clock cycles (POR reset value).
0xF
31:4
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-
Table 422. Dynamic Memory Active to Precharge Command Period register (DYNAMICRAS,
address 0x4000 5034) bit description
Bit
Symbol
Description
Reset
value
3:0
TRAS
Active to precharge command period.
0x0 - 0xE = n + 1 clock cycles. The delay is in EMC_CCLK cycles.
0xF = 16 clock cycles (POR reset value).
0xF
31:4
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-