Chapter 9. SDRAM Controller
9-15
Solving Timing Issues with SDCR[INV]
If the delay between shifted SDCLK and following internal system clock edge is shorter
than the read access time of the SDRAM, data is sampled with the true CAS latency.
Figure 9-7. Timing Refinement with True CAS Latency and Inverted SDCLK
Selecting a system clock frequency low enough that the SDCLK-to-CLK delay is long
compared to the SDRAM read access time reduces effective CAS latency by 1 cycle.
Figure 9-8. Timing Refinement with Effective CAS Latency
NOTE:
When reduced effective CAS latency is used, the SDRAM is
still programmed with true CAS latency. The SDRAM
controller state machine must be reprogrammed for the
reduced CAS latency. SDRAM initialization software
Shifted delay of SDCLK
Delay SDCLK to CLK
SDRAM read access time
T
SDCLK_to_CLK
- T
acc
< 0 => true CAS latency
CASL = 2
Internal
CLK
Data
SDCLK
Shifted delay of SDCLK
Delay SDCLK to CLK
SDRAM read access time
T
SDCLK_to_CLK
- T
acc
> 0 => effective CAS latency reduced by 1
CASL = 1
SDCLK
Data
Internal CLK
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 ...