6-46
MPC106 PCIB/MC User's Manual
MOTOROLA
Note that any unused banks should have their starting and ending addresses programmed
out of the range of memory banks in use. If a disabled bank has its starting and ending
address defined as overlapping an enabled bank’s address space, there may be system
memory corruption in the overlapping address range. Always map unused memory banks’
starting and ending addresses to memory space that is not used by the system.
Once all the memory parameters are configured, then system software should set the
MEMGO bit (MCCR1, bit 19) to enable the memory interface. (Note that 100
μ
s must
elapse after the negation of HRST before the MEMGO bit can be set, so a delay loop in the
initialization code may be necessary.)
The MPC106 then proceeds with the following initialization sequence:
1. Issues a precharge-all-banks command
2. Issues eight refresh commands
3. Issues a mode-set command to initialize the mode register
See Section 6.4.6, “JEDEC Standard SDRAM Interface Commands,” for detailed
information about the SDRAM commands in the above sequence. When the sequence
completes, the SDRAM array is ready for access.
6.4.6 JEDEC Standard SDRAM Interface Commands
The MPC106 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 60x bus clock. Data at the output of the SDRAM device must be sampled
on the rising edge of the 60x bus clock.
The MPC106 provides the following SDRAM interface commands:
Activate-bank—Latches the row address and initiates a memory read of that row.
Row data is latched in SDRAM sense amplifiers and must be restored by issuing a
precharge command before another bank-activate is issued.
Precharge-bank—Restores data from the sense amplifiers to the appropriate row.
Also initializes the sense amplifiers in preparation for reading another row in the
SDRAM internal bank. A precharge command must be issued after a read or write,
if the row address changes on the next access. Note that the MPC106 uses SDMA1
to distinguish between the precharge-bank and precharge-all-banks commands. The
SDRAMs must be compatible with this format.
Precharge-all-banks—Initializes the sense amplifiers of all SDRAM internal banks.
Note that the MPC106 uses SDMA1 to distinguish between the precharge-all-banks
and precharge-bank commands. The SDRAMs must be compatible with this format.
Read—Latches the column address and transfers data from the selected sense
amplifier to the output buffer as determined by the column address. During each
succeeding clock, additional data is output without additional read commands. The
amount of data transferred is determined by the burst size.