Freescale Semiconductor MCF5480 - Manual (Page 470)

MCF548x Reference Manual, Rev. 3
18-22 Freescale Semiconductor
The minimum values of certain fields can be different for SDR and DDR SDRAM, even if the data sheet
timing is the same, because:
• In SDR mode, the memory controller counts the delay in SDCLK
• In DDR mode, the memory controller counts the delay in SDCLK × 2
SDCLK—memory controller clock—is the speed of the SDRAM interface and is equal to the internal bus
clock.
SDCLK
× 2—double frequency of SDCLK—DDR uses both edges of the bus-frequency clock (SDCLK)
to read/write data
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
R SRD2RW 0 SWT2RD RDLAT 0 ACT2RW
W
Reset Uninitialized
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
R 0 PRE2ACT REF2ACT 0 WTLAT 0 0 0 0
W
Reset Uninitialized
Reg
Addr
MBAR + 0x0108
Figure 18-12. SDRAM Configuration Register 1 (SDCFG1)
Table 18-12. SDCFG1 Field Descriptions
Bits Name Description
31–28 SRD2RW Single Read to Read/Write/Precharge delay. Limiting case is usually Write to Precharge.
DDR mode:
SRD2RW = CASL + (BL/2) + 1
For DDR, suggested value = 0x7
SDR mode:
SRD2RW = CASL + BL + 1
If CASL=2, suggested value = 0xB
If CASL=3, suggested value = 0xC
27 — Reserved. should be cleared
26–24 SWT2RD Single Write to Read/Write/Precharge delay. Limiting case is Write to Precharge.
DDR mode:
SWT2RD = t
WR
/SDCLK + 1, suggested value = 0x3
SDR mode:
SWT2RD = t
WR
, suggested value = 0x2
23–20 RDLAT Read CAS Latency. Read latency. Read command to read data available delay counter.
DDR mode:
If CASL = 2, write 0x6
If CASL = 2.5, write 0x7
SDR mode:
If CASL = 2, write 0x2
If CASL = 3, write 0x3
Note: CASL=2.5 is not supported for SDR.