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SDRAM Controller
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
9-15
NOTE
The SDRAM shares address and data signals with external memory and
peripherals. Due to stringent SDRAM timing requirements, it is strongly
recommended to buffer the address, byte strobe, and data buses between the
MCF5272 and non-SDRAM memory and peripherals. Never buffer signals
to the SDRAMs. See Appendix C for details on how to buffer external
memory and peripherals in a system using SDRAM.
The controller allows single-beat read/write accesses and the following burst accesses:
•
16-byte cache line read bursts from 32-bit wide SDRAM with access times of
n
-1-1-1. The value
of
n
depends on read, write, page miss, page hit, etc. The enable extended bursts bit in chip select
option register 7 (CSOR7[EXTBURST]) must be cleared, CSBR7[EBI] must be set for SDRAM,
and CSBR7[BW] must be set for a 16-byte cache line width.
•
16-byte cache line read bursts from 16-bit wide SDRAM with access times of
n
-1-1-1-1-1-1-1.
CSOR7[EXTBURST] must be set, CSBR7[EBI] must be set for SDRAM, and CSBR7[BW] must
be set for 16 bits.
•
16-byte read or write bursts during Ethernet DMA transfers to/from SDRAM with access times of
n
-1-1-1 or
n
-1-1-1-1-1-1-1 depending on 32 or 16 bit SDRAM port width as described in the
previous two paragraphs.
These SDRAM accesses are shown in
low-power, self-refreshing sleep mode as shown in
off the SDRAM controller completely using the power management control register in the SIM.
Figures show burst read and burst writes, with a page miss and a page hit for each case. A single-cycle read
or write is identical to the first access of a burst. In normal operation the SDRAM controller refreshes the
SDRAM.
As these examples show, SDCLKE is normally high and SDCLK is always active. SDCLKE can be forced
to 0 and SDCLK can be shut off by putting the SDRAM controller into power down or self-refresh mode.
9.10.1
SDRAM Read Accesses
The read examples,
, show a CAS latency of 2, SDCR[REG] = 0 and
SDCR[INV] = 1.
In T1, the ColdFire core issues the address. This cycle is internal to the device and always occurs. In T2,
the SDRAM controller determines if there is a page miss or hit. This cycle is internal to the device and
always occurs.
PRECHARGE
command (T3) and the following cycle occur.
During precharge the SDRAM writes the designated on-chip RAM page buffer back into the SDRAM
array. The number of cycles for a precharge is set by programming SDTR[RP]. The default after reset is
two cycles. The activate new page cycle that follows (T5) is required to open a new page due to the page
miss. Cycle T6 is a wait state for SDRAM activation command. It is added due to default value of 0b01 in
SDTR[RCD]. For lower clock speed systems the RCD value could be written as 00 and this clock cycle
can be removed. Consult the data sheets of the SDRAM devices being used.