UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
496 of 1269
NXP Semiconductors
UM10503
Chapter 21: LPC43xx External Memory Controller (EMC)
The read address is calculated as follows:
•
Determine the mode register content MODE:
–
For a single 16-bit external SDRAM chip set the burst length to 8. For a single
32-bit SDRAM chip set the burst length to 4.
–
Select the sequential mode.
–
Select latency mode = 2 or 3.
–
Select Write burst mode = 0.
•
Determine the shift value OFFSET to shift the mode register content by. This shift
value depends on the SDRAM device organization and it is calculated as:
OFFSET = number of c total bus width + bank select bits
–
The number of columns is listed in
for a specific SDRAM device.
–
The total bus with is 1 for a 16-bit bus and 2 for a 32-bit bus. If you combine two
16-bit devices to form a 32-bit memory bank, the total bus width is 2.
–
This is the number of bits needed to indicate the number of banks. Most SDRAM
devices use 2 bank select bits for four banks.
•
Select the SDRAM memory mapped address DYCSX.
•
The SDRAM read address is ADDRESS = DYCSX + (MODE << OFFSET).
21.8.5.2.1
Example for setting the SDRAM mode register
For a 16-bit external SDRAM chip, select latency mode = 2 and burst size = 8. The mode
register value is MODE = 0x23.
Using a 128 Mb (8Mx16) SDRAM chip with address mapping of 4 banks, row length = 12,
column length = 9 (see
), OFFSET = 9 + 1 + 2.
Using DYCS0, the SDRAM address is 0x2800 0000.
The SDRAM read command address becomes 0x2802 3000.
21.8.5.3 Self-refresh mode
The EMC provides a mechanism to place the dynamic memories into self-refresh mode.
Self-refresh mode can be entered by software by setting the SREFREQ bit in the
DynamicControl Register and polling the SREFACK bit in the Status Register.
Any transactions to memory that are generated while the memory controller is in
self-refresh mode are rejected and an error response is generated to the AHB bus.
Clearing the SREFREQ bit in the DynamicControl Register returns the memory to normal
operation. See the memory data sheet for refresh requirements.
Note: The static memory can be accessed as normal when the SDRAM memory is in
self-refresh mode.