
SDRAM Controller
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
9-12
Freescale Semiconductor
, the timing configuration is RTP = 61, RC = negligible, RCD = 0, RP = 0, and CLT = 1.
9.9
Solving Timing Issues with SDCR[INV]
When some SDRAM devices (such as 4 x 8 bit wide SDRAMs) are used, the SDCLK and other control
signals are more loaded than data signals. In normal MCF5272 operation, the write data and all other
control signals change with the positive edge of SDCLK. Large 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
Table 9-13. SDRAM Controller Performance, 16-Bit Port, (RCD=0, RP=0)
SDRAM Access
Number of System Clock Cycles
REG = 0, INV = 0
REG = 1, INV = 0
Single-beat read Page miss
7
8
Page hit
5
6
Single-beat
longword read
Page miss
7-1
8-1
Page hit
5-1
6-1
Single-beat write Page miss
5
5
Page hit
3
3
Single-beat
longword write
Page miss
5-1
5-1
Page hit
3-1
3-1
Burst read
Page miss
7-1-1-1-1-1-1-1 = 14
8-1-1-1-1-1-1-1 = 15
Page hit
5-1-1-1-1-1-1-1 = 12
6-1-1-1-1-1-1-1 = 13
Burst write
Page miss
5-1-1-1-1-1-1-1 = 12
5-1-1-1-1-1-1-1 = 12
Page hit
3-1-1-1-1-1-1-1 = 10
3-1-1-1-1-1-1-1 = 10
External delay of SDCLK
Data setup delay
Internal CLK
Data bus
SDCLK