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SDRAM Controller (SDRAMC)
Freescale Semiconductor
21-27
The RCR delay module maintains the 1/4 memory clock period delay of the DQS signals across the full
range of silicon process, voltage, and temperature conditions.
The RD_CLK is an internal reconstructed clock derived from DQS. It is twice the frequency of DQS, with
the rising edge shifted 1/4 memory clock period after the DQS edge to align with the nominal center of the
data valid window.
21.6
Initialization/Application Information
SDRAMs have a prescribed initialization sequence. The following sections detail the memory
initialization steps for DDR SDRAM, mobile DDR, and DDR2 SDRAM. The sequence might change
ghtly from device-to-device. Refer to the SDRAM manufacturer’s device datasheet as the most relevant
reference.
21.6.1
DDR SDRAM Initialization Sequence
1. After reset is deactivated, pause for the amount of time indicated in SDRAM specification. Usually
200
s.
2. Configure pin multiplex control for shared SD_CS pins in pin multiplexing and control module if
needed.
3. Configure the slew rate for the SDRAM external pins in the pin multiplexing and control module’s
MSCR_SDRAM register if needed.
4. Write the SDCS
n
register values for each chip select that is used.
5. Program SDRAM configuration registers (SDCFG1 and SDCFG2) with correct delay and timing
values.
6. Issue a
PALL
command. Initialize the SDRAM control register (SDCR) with SDCR[IPALL] and
SDCR[MODE_EN] set. The SDCR[REF and IREF] bits should remain cleared for this step.
7. Initialize the SDRAM’s extended mode register to enable the DLL. See
Mode/Extended Mode Register Command (lmr, lemr),”
for instructions on issuing a
LEMR
command.
8. Initialize the SDRAM’s mode register and reset the DLL using the
LMR
command. See
Section 21.5.1.6, “Load Mode/Extended Mode Register Command (lmr, lemr),”
for more
instruction on issuing a
LMR
command. During this step the OP_MODE field of the mode register
should be set to normal operation/reset DLL.
9. Pause for the DLL lock time specified by the memory.
10. Issue a second
PALL
command. Initialize the SDRAM control register (SDCR) with SDCR[IPALL]
and SDCR[MODE_EN] set. The SDCR[REF and IREF] bits should remain cleared for this step.
11. Refresh the SDRAM. The SDRAM specification should indicate a number of refresh cycles to be
performed before issuing an
LMR
command (usually two). Write to the SDCR with the IREF and
MODE_EN bits set (SDCR[REF and IPALL] must be cleared). This forces a refresh of the
SDRAM each time the IREF bit is set. Repeat this step until the specified number of refresh cycles
have been completed.
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...