UM10503
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
477 of 1269
NXP Semiconductors
UM10503
Chapter 21: LPC43xx External Memory Controller (EMC)
For example, for the refresh period of 16 µs, and a CCLK frequency of 50 MHz, the
following value must be programmed into this register:
(16 x 10
-6
x 50 x 10
6
) / 16 = 50 or 0x32
If auto-refresh through warm reset is requested (by setting the EMC_Reset_Disable bit),
the timing of auto-refresh must be adjusted to allow a sufficient refresh rate when the
clock rate is reduced during the wake-up period of a reset cycle. During this period, the
EMC (and all other portions of the chip that are being clocked) run from the IRC oscillator
at 12 MHz. The IRC oscillator frequency must be used as the CCLK rate for refresh
calculations if auto-refresh through warm reset is requested.
Note: The refresh cycles are evenly distributed. However, there might be slight variations
when the auto-refresh command is issued depending on the status of the memory
controller.
21.7.6 Dynamic Memory Read Configuration register
The DYNAMICREADCONFIG register configures the dynamic memory read strategy.
This register must be modified during system initialization with a bit value RD
1. 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.
Remark:
Choose command delay strategy (RD = 0x1) for SDRAM operation.
See
for programming the delay value for the EMC_CLKn delay.
Table 358. Dynamic Memory Refresh Timer register (DYNAMICREFRESH - address
0x4000 5024) bit description
Bit
Symbol
Description
Reset
value
10:0
REFRESH
Refresh timer.
Indicates the multiple of 16 CCLKs between SDRAM refresh cycles.
0x0 = Refresh disabled (POR reset value).
0x1 - 0x7FF = n x16 = 16n CCLKs between SDRAM refresh cycles.
For example:
0x1 = 1 x 16 = 16 CCLKs between SDRAM refresh cycles.
0x8 = 8 x 16 = 128 CCLKs between SDRAM refresh cycles
0
31:11 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-