參數(shù)資料
型號: PPC440GR-3pbfffCx
廠商: Applied Micro Circuits Corp.
英文描述: Power PC 440GR Embedded Processor
中文描述: 440GR的Power PC嵌入式處理器
文件頁數(shù): 74/82頁
文件大?。?/td> 527K
代理商: PPC440GR-3PBFFFCX
74
AMCC Proprietary
Revision 1.16 – July 19, 2006
Preliminary Data Sheet
440GR – PPC440GR Embedded Processor
DDR SDRAM Read Operation
The following examples of timing for DDR SDRAM read operations are based on the relationship between the
incoming data and the PLB clock signal. Since the PLB clock cannot be directly observed, the delay of
MemClkOut(0) relative to the PLB clock (T
MD
) is provided.
The internal Read Clock signal, like MemClkOut0, is derived from the PLB clock and can be delayed relative to the
PLB clock by programming the RDCT and RDCD fields in the SDRAM0_TR1 register. The delay can be
programmed from 0 to 1/2 cycle in steps using RDCT. Setting RDCD results in a 1/2 cycle delay plus the value set
in RDCT. The delay of Read Clock relative to the PLB clock (T
RD
) shown below assumes the programmable Read
Clock delay is set to zero.
Figure 9. DDR SDRAM MemClkOut0 and Read Clock Delay
In operation, following the receipt of an address and read command from the PPC440GR, the SDRAM generates
data and the DQS signals coincident with MemClkOut0. The data is latched into the PPC440GR using a DQS
signal that is delayed 1/4 of a cycle. In order to accommodate timing variations introduced by the system designs
using this chip, the three-stage data path shown below is used to eliminate metastability and allow data sampling to
be adjusted for minimum latency. This adjustment requires programming the Read Clock delay and the selection of
Stage 1, Stage 2, or Stage 3 data for sampling at RDSP.
Read Clock
PLB Clk
MemClkOut0(0)
T
MD
T
RD
T
MD
min = 600ps
T
MD
max = 1100ps
T
RD
min = 300ps
T
RD
max = 740ps
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