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SDRAM Controller
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
9-13
shows timing relationships between SDCLK and the remaining data and control signals can
be refined by setting SDCR[INV], which inverts the SDRAM clock. SDCR[REG] must always be cleared
when SDCR[INV] is set.
.
Figure 9-6. Timing Refinement with Inverted SDCLK
NOTE
If the delay difference between the fastest data signal and the slowest control
signal exceeds half of the clock cycle time, the clock shift can cause
hold-time violations on control signals.
The incoming data setup time should be inspected during reads. The active clock edge event of SDCLK
now precedes the MCF5272 internal active clock edge event when (REG = 0). This behavior is frequency
dependent. The two following scenarios are possible:
•
High-speed timing refinement with true CAS latency. See
•
Low-speed timing refinement with reduced effective CAS latency.
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
Shifted delay of SDCLK
Data setup delay
Internal CLK
Data bus
SDCLK
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