Chapter 9. SDRAM Controller
9-17
SDRAM Interface
•
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 Figure 9-9 through Figure 9-15. The SDRAM
supports a low-power, self-refreshing sleep mode as shown in Figure 9-14 and Figure 9-15.
It is also possible to turn 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, Figure 9-9 and Figure 9-10, 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.
Because Figure 9-9 shows a page miss, the
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.
Содержание DigitalDNA ColdFire MCF5272
Страница 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
Страница 38: ...xxxviii MCF5272 User s Manual TABLES Table Number Title Page Number ...
Страница 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Страница 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Страница 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Страница 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Страница 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Страница 338: ...13 44 MCF5272 User s Manual Application Examples ...
Страница 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Страница 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Страница 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Страница 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...
Страница 548: ...INDEX Index 12 MCF5272 User s Manual ...