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UM10503
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User manual
Rev. 2.1 — 10 December 2015
609 of 1441
NXP Semiconductors
UM10503
Chapter 23: LPC43xx/LPC43Sxx External Memory Controller (EMC)
23.7.14 Dynamic Memory Auto-refresh Period register
This 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.
23.7.15 Dynamic Memory Exit Self Refresh register
This 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.
23.7.16 Dynamic Memory Active Bank A to Active Bank B Time register
This 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.
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 428. 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 EMC_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 429. 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 EMC_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.
-