SDRAM Example
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 18-25

18.8.1 SDRAM Signal Drive Strength Settings

The SDRAMDS should be programmed as shown in Figure 18-14. The settings assume the normal drive

strength for 2.5V drive, 7.6mA, is sufficient for the loading in the system.

This configuration results in a value of SDRAMDS = 0x0000_02AA, as described in Table 18-15.

18.8.2 SDRAM Chip Select Settings

For this example, the SDRAM will be connected to SDCS0 with a base address of 0x0. All other chip

selects are unused and do not need to be initialized. The CS0CFG should be programmed as shown in

Figure 18-15.

Write recovery timer (tWR)15 ns
Precharge command to ACTV command (tRP) 15 ns (min) 18ns (max)
Auto refresh command period (tRFC) 72ns (min) 75ns (max)
Average periodic refresh interval (tREFI)7.8 µs
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Field —
Setting 0000_0000_0000_0000
(hex) 0 0 0 0
1514131211109876543210
Field — SB_E SB_C SB_A SB_S SB_D
Setting 0000_0010_1010_1010
(hex) 0 2 A A

Figure 18-14. SDRAM Example Drive Strength Settings (SDRAMDS)

Table 18-15. SDRAMDS Field Descriptions

Bits Name Setting Description
31–10 0 Reserved. Should be cleared
9–8 SB_E 10 2.5V, 7.6mA SSTL_2 Class I drive
7–6 SB_C 10 2.5V, 7.6mA SSTL_2 Class I drive
5–4 SB_A 10 2.5V, 7.6mA SSTL_2 Class I drive
3–2 SB_S 10 2.5V, 7.6mA SSTL_2 Class I drive
1–0 SB_D 10 2.5V, 7.6mA SSTL_2 Class I drive

Table 18-14. SDRAM Example Specifications (Continued)

Parameter Specification