MPC5200B Users Guide, Rev. 1
8-22 Freescale Semiconductor
Memory Controller Registers (MBAR+0x0100:0x010C)
8.7.2 Control Register—MBAR + 0x0104
The 32-bit read/write Control register controls specific operations and generates some SDRAM commands. This register is reset only by a
power-up reset signal.
Table8-6. Memory Controller Control Register
msb 01 2 345678 9101112131415
R mode
_en
cke ddr re f
_en
Rsvd hi_
addr
Rsvd drive
_rule
ref_interval[0:5]
W
RESET:00 0 000000 0 0 000 0 0
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 lsb
RReserved mem_
ps
Rsvd dqs_oe Reserved Rsvd
Wsoft
_ref
soft
_pre
RESET:00 0 000000 0 0 000 0 0
Bit Name Description
0 mode_en 0 Mode register locked, cannot be written.
1 Mode register enabled, can be written.
1 cke 0 MEM_CLK_EN negated (low).
1 MEM_CLK_EN asserted (high).
cke must be set to 1 to perform normal read and write operations. Set cke to 0 to put the
memory in Self Refresh or Power Down mode.
2 ddr 0 SDR mode.
1 DDR mode.
3 ref_en 0 Automatic refresh disabled.
1 Automatic refresh enabled.
In general, refresh must be enabled, unless the system is known to access memory in a
pattern that is guaranteed to open every row in every bank within every refresh period
tREF
. Some memory data sheets do not spec tREF
, but spec tREFI instead. In this case, tREF
= tREFI x #rows.
NOTE: The number of Refresh commands required in tREF is #rows; if refresh is disabled,
the number of Read/Write commands required in tREF is #rows x 4banks.
4:6 — Reserved
7 hi_addr Control the use of internal address bits XLA[4:7] as row or column bits on the MEM_MA
bus. See Ta b l e 8- 7 .
8 Reser ved (must be written 0)
9 drive_rule 0 “Tri-state except to write” mode: MPC5200B drives the MDQ and MDQS lines only
when necessary to perform write commands.
1 “Dr ive except to read” mode: MPC5200B tri-states the MDQ and MDQS lines only
when necessary to perform read commands.
“Drive except to read” mode prevents unterminated memory signals from floating for
extended periods. However, terminated routing is always recommended over
unterminated.