Motorola MPC8260 - Manual (Page 311)

MOTOROLA Chapter 10. Memory Controller 10-35
Part III. The Hardware Interface
10.4.1 Supported SDRAM ConÞgurations
The MPC8260 memory controller supports any SDRAM conÞguration under the
restrictions that all SDRAM devices that reside on the same bus (60x or local) should have
the same port size and timing parameters.
10.4.2 SDRAM Power-On Initialization
At system reset, initialization software must set up the programmable parameters in the
memory controller banks registers (ORx, BRx, P/LSDMR). After all memory parameters
are conÞgured, system software should execute the following initialization sequence for
each SDRAM device.
1. Issue a PRECHARGE - ALL - BANKS command
2. Issue eight CBR REFRESH commands
3. Issue a MODE - SET command to initialize the mode register
The initial commands are executed by setting P/LSDMR[OP] and accessing the SDRAM
with a single-byte transaction. See Figure 10-10.
Note that software should ensure that no memory operations begin until this process
completes.
10.4.3 JEDEC-Standard SDRAM Interface Commands
The MPC8260 performs all accesses to SDRAM by using JEDEC-standard SDRAM
interface commands. The SDRAM device samples the command and data inputs on the
rising edge of the MPC8260 bus clock. Data at the output of the SDRAM device must be
sampled on the rising edge of the MPC8260 bus clock.
The MPC8260 provides the following SDRAM interface commands:
Table 10-18. SDRAM Interface Commands
Command Description
BANK - ACTIVATE Latches the row address and initiates a memory read of that row. Row data is latched in SDRAM
sense ampliÞers and must be restored with a
PRECHARGE command before another BANK - ACTIVATE is
issued.
MODE - SET Allows setting of SDRAM optionsÑCAS latency, burst type, and burst length. CAS latency depends
on the SDRAM device used (some SDRAMs provide CAS latency of 1, 2, or 3; some provide a latency
of 1, 2, 3, or 4, etc.). Burst type must be chosen according to the 60x cache wrap (sequential).
Although some SDRAMs provide burst lengths of 1, 2, 4, 8, or a page, MPC8260 supports only a
4-beat burst for 64-bit port size and an 8-beat burst for 32-bit port size. MPC8260 does not support
burst lengths of 1, 2, and a page for SDRAMs. The mode register data (CAS latency, burst length, and
burst type) is programmed into the P/LSDMR register by initialization software at reset. After the P/
LSDMR is set, the MPC8260 transfers the information in the SDMODE Þeld to the SDRAM array by
issuing a
MODE - SET command. Section 10.4.9, ÒSDRAM Mode-Set Command Timing,Ó gives timing
information.