MCF548x Reference Manual, Rev. 3
18-4 Freescale Semiconductor

18.3.12 SDRAM Clock Enable (SDCKE)

This output is the SDRAM clock enable. SDCKE negates to put the SDRAM into low-power, self-refresh
mode.

18.3.13 SDR SDRAM Data Strobe (SDRDQS)

This is connected to SDDQS inputs. It is used in SDR mode only.

18.3.14 SDRAM Memory Supply (SDVDD)

These pins supply positive power to the SDRAM module. SDVDD should be connected to +2.5V for DDR
operation and +3.3V for SDR.

18.3.15 SDRAM Reference Voltage (VREF)

This is the input reference voltage for differential SSTL_2 inputs. It is used in both DDR and SDR modes.
For DDR VREF should be connected to 1.25V, and for SDR VREF should be connected to 1.5V.

18.4 Interface Recommendations

18.4.1 Supported Memory Configurations

The SDRAM controller supports up to 13 row addresses and up to 12 column addresses. However, the
maximum row and column addresses are not supported at the same time. The number of row and column
addresses must be less than or equal to 24. In addition to row/column address lines, there are always two
row bank address bits. Therefore, the greatest possible address space which can be accessed using a single
chip select is (226) x 32 bits, or 256 Mbytes.
Table 18-2 shows the address multiplexing used by the MCF548x for different configurations. When the
SDRAM controller receives the internal module enable, it latches the internal bus address lines addr[27:2]
and multiplexes them into row, column and row bank addresses. addr[9:2] are always used for CA[7:0],
addr[11:10] are always used for BA[1:0], and addr[23:12] are always used for RA[11:0]. addr[27:24] can
be used for additional row or column address bits, as needed.
NOTE
The SDRAMC only supports an external 32-bit data bus. It is not possible
to connect a smaller device(s) to only part of the SDRAM’s data bus. For
example, if 16-bit wide devices are used, then you must use two 16-bit
devices connected as a 32-bit port.