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SDRAM Controller (SDRAMC)
21-30
Freescale Semiconductor
If a new access does not fall in the open row of an open bank of a SD_CS block, the open row must be
closed (
PRE
) and the new row must be opened (
ACTV
), then the
READ
or
WRITE
command can proceed. An
ACTV
command activates only one bank at one time. If another read or write falls in an inactive bank,
another
ACTV
is needed, but no precharge is needed. If a read or write falls in any open row of any active
banks of a page, no
PRE
or
ACTV
is needed; the read or write command can be issued immediately.
A page is kept open until one of the following conditions occurs:
•
An access outside the open page.
•
A refresh cycle is started.
All SD_CS blocks are refreshed at the same time. The refresh closes all banks of every SDRAM block.
21.6.5
Transfer Size
In the SDRAMC, the internal data bus is 32 bits wide, while the SDRAM external interface bus is 16 bits
wide. Therefore, each internal data beat requires two memory data beats. The SDRAM controller manages
the size translation (packing/unpacking) between internal and external DRAM buses.
The burst size is the processor standard 16 bytes: Four beats of 4 bytes on the internal bus or eight beats
of 2 bytes (16-bit mode) on the memory bus. The SDRAM controller follows the critical beat first,
sequential transfer format required.
The burst size and transfer order must be programmed in the SDRAM mode registers during initialization;
the burst size also must be programmed in the memory controller (SDCFG2 register).
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 ...