9-14
MCF5272 User’s Manual
Solving Timing Issues with SDCR[INV]
capacitive loads on SDCLK can cause long delays on SDCLK, possibly causing SDRAM
hold-time violations during writes. The clock may arrive at the same time as the write data.
The write data setup time to SDCLK edge may not meet device requirements at the
SDRAM. This timing issue cannot be solved by reducing the SDCLK frequency. SDCLK
must be delayed further to meet setup/hold margin on the SDRAM data input. Setting INV
provides a 180° phase shift and moves the positive clock edge far beyond the data edge.
Figure 9-5. Example Setup Time Violation on SDRAM Data Input during Write
As Figure 9-6 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 Figure 9-7.
•
Low-speed timing refinement with reduced effective CAS latency.
External delay of SDCLK
Data setup delay
Internal CLK
Data bus
SDCLK
Shifted delay of SDCLK
Data setup delay
Internal CLK
Data bus
SDCLK
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 ...