Freescale Semiconductor MPC8260 11.4.9 SDRAM MODE-SET Command Timing, 11.4.10 SDRAM Refresh

Memory Controller
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 11-47
11.4.9 SDRAM MODE-SET Command Timing
The PowerQUICC II transfers mode register data (CAS latency, burst length, burst type) stored in
P/LSDMR to the SDRAM array by issuing the MODE-SET command. Figure 11-37 shows timing for the
MODE-SET command.
Figure 11-37. SDRAM MODE-SET Command Timing
Figure 11-38 shows mode data bit settings.
Figure 11-38. Mode Data Bit Settings
11.4.10 SDRAM Refresh
The memory controller supplies auto (CBR) refreshes to SDRAM according to the interval specified in
PSRT or LSRT . This represents the time period required between refr eshes. The value of P/LSR T depends
on the specific SDRAM devices used and the operating frequency of the PowerQUICC II’s bus. This value
should allow for a potential collision between memory accesses and refresh cycles. The period of the
refresh interval must be greater than the access time to ensure that read and write operations complete
successfully.
CLK
ALE
CS
SDRAS
SDCAS
MA[0–11]
WE
DQM
Data ZZ
D0 D1 D2 D3
*Mode Data Row Column
*The mode data is the address value during a mode-set cycle. It is driven by the memory controller, in single
PowerQUICCII mode, according to P/LSDMR[CL] register. In 60x-compatible mode, software must drive the
correct value on the address lines. Figure11-38. shows the actual value.
Mode Set Page Activate Write (Burst)
latency mode—can be 1(001), 2(010), or 3(011).
burst length:
4(010) for 16- and 64-bit port sizes
8(011) for 8- and 32-bit port sizes
Bit number01234567891011lsb
CL 0 BL