UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
95 of 362
NXP Semiconductors
UM10208
Chapter 8: LPC2800 EMC
[1]
CLKOUT can be disabled if there are no SDRAM memory transactions. When enabled this bit can be used
in conjunction with the dynamic memory clock control (CS) field.
10.5 Dynamic Memory Refresh Timer Register (EMCDynamicRefresh -
0x8000 8024)
The EMCDynamicRefresh Register controls refresh timing for dynamic memory. This
register should only be 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. However, these control bits can, if necessary, be
altered during normal operation. This register is accessed with one wait state.
shows the EMCDynamicRefresh Register.
For example, for a refresh period of 16 µs, and an HCLK frequency of 50 MHz, the
following value must be programmed into this register:
(16
×
10
-6
×
50
×
10
6
) / 16 = 50 or 0x32
If refresh through warm reset is requested (by setting the EMC_Reset_Disable bit), the
refresh timing must be adjusted to allow a sufficient refresh rate when the clock rate is
reduced during the wakeup period of a reset cycle. During this period, HCLK runs at
12 MHz. Therefore 12 MHz must be considered the clock rate for refresh calculations, if
refresh through warm reset is desired.
Note: Refresh cycles are evenly distributed, but there might be slight variations in the
timing of refresh cycles, depending on the status of the memory controller.
13
DP
Write a 1 to this bit to enter SDRAM deep power down mode. See
“Low-power SDRAM Deep-sleep mode” on page 88 for more
information.
0
15:14 RPOUT
Control
This field controls the RPOUT signal to reset Micron-compatible
SyncFlash memory:
0x: 0V
10: 3V
11: do not write this value
31:16 -
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
-
Table 81.
Dynamic Control Register (EMCDynamicControl - address 0x8000 8020)
Bit
Symbol
Description
POR
Reset
Value
Table 82.
Dynamic Memory Refresh Timer Register (EMCDynamicRefresh - 0x8000 8024)
Bit
Symbol
Description
POR
Reset
Value
10:0
REFRESH When this field is 000, as it is after a power-on reset, dynamic memory
refresh cycles are not performed (note that power-on reset sets
self-refresh mode). Otherwise this field selects the refresh period, in
units of 16 AHB HCLK cycles. That is, 0x001 sets the refresh period as
16 HCLKs, 0x002 sets it as 32 HCLKS, and so on.
0x000
31:11 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-