Chapter 6. MPC8240 Memory Interface
6-33
SDRAM Interface Operation
6.2.12.1 SDRAM Refresh Timing
The CBR refresh timing for SDRAM is controlled by the programmable timing parameter
MCCR3[REFREC]. REFREC represents the number of clock cycles from the refresh
command until a bank-activate command is allowed. The AC specifications of the specific
SDRAM device provides a minimum refresh-to-activate interval.
The MPC8240 implements bank staggering for CBR refreshes, as shown in Figure 6-18.
This reduces instantaneous current consumption for memory refresh operations.
Figure 6-18. SDRAM Bank Staggered CBR Refresh Timing
6.2.12.2 SDRAM Refresh and Power Saving Modes
The MPC8240’s memory interface provides for sleep, doze, and nap power saving modes
defined for the local processor architecture. See Chapter 14, “Power Management,” for
more information on these modes.
In doze and nap power saving modes, the MPC8240 supplies normal CBR refresh to
SDRAM. In sleep mode, the MPC8240 can be configured to use the SDRAM self-refresh
mode, provide normal refresh to SDRAM, or provide no refresh support. If the MPC8240
is configured to provide no refresh support in sleep mode, system software is responsible
for appropriately preserving SDRAM data, such as by copying to disk. Table 6-14
summarizes the MPC8240configuration bits relevant to power-saving modes.
SDRAM
CKE
CS[0,7]
CS[1,6]
CS[2,5]
SDRAS
CS[3,4]
SDCAS
ACTORW
NOTE: Only one CS signal is asserted for the bank-activate and read commands.
CLK[0:3]
WE
DQM[0:7]
ROW ADDR
COL ADDR
SDBA0
SDMA[12:0]
REFREC
* See note
Содержание MPC8240
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Страница 466: ...13 12 MPC8240 Integrated Processor User s Manual Exception Latencies ...
Страница 516: ...16 14 Watchpoint Trigger Applications ...
Страница 538: ...B 16 MPC8240 Integrated Processor User s Manual Setting the Endian Mode of Operation ...
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Страница 640: ...INDEX Index 16 MPC8240 Integrated Processor User s Manual ...