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SDRAM Controller (SDRAMC)
Freescale Semiconductor
21-29
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. For DDR2, write zeroes to the extended mode registers 2 and 3.
8. 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.
9. 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.
10. Pause for the DLL lock time specified by the memory.
11. 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.
12. 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.
13. Initialize the SDRAM’s mode register using the
LMR
Mode/Extended Mode Register Command (lmr, lemr),”
for more instruction on issuing an
LMR
command. During this step the OP_MODE field of the mode register should be set to normal
operation.
14. Set SDCR[REF] to enable automatic refreshing, and clear SDCR[MODE_EN] to lock the SDMR.
SDCR[IREF and IPALL] remain cleared.
21.6.4
Page Management
SDRAM devices have four internal banks. A particular row and bank of memory must be activated to
allow read and write accesses. The SDRAM controller supports paging mode to maximize the memory
access throughout. During operation, the SDRAM controller maintains an open page for each SD_CS
block. An open page is composed of the active rows in the internal banks. Each internal bank has its own
active row.
The physical page size of a SD_CS block is equal to the space size divided by the number of rows; but the
page may not be contiguous in the internal address space because SDRAMs can have a different row
address open in each bank and the internal address bits (A[27:24] and A[9:2]) or (A[27:24] and A[9:1])
used for memory column addresses are not consecutive.
Because the column address may split across two portions of the internal address, the contiguous page size
is (number of contiguous columns per bank)
(number of bits). This gives a contiguous page size of
1 KBytes. However, the total (possibly fragmented) page size is (number of banks)
(number of
columns)
(number of bits).
Содержание MCF54455
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