Philips Semiconductors
SDRAM Memory System
File: memsys.fm5, modified 7/24/99
PRELIMINARY INFORMATION
11-3
11.5.1
MM_CONFIG Register
The MM_CONFIG register tells the memory interface
how to use the local DRAM memory. The fields in this
register tell the interface the rank size and the refresh
rate of the memory.
Table 11-6 summarizes the field
functions.
REFRESH (Refresh interval). The 16-bit REFRESH
field specifies the number of memory-system clock cy-
cles between refresh operations. The default value of
Bit three of MM_CONFIG must be set to zero for normal
operation.
SIZE (Rank Size). The three-bit SIZE field specifies the
size of each rank of DRAM. Each rank must be the size
specified by SIZE. The default is a rank size of 4MB. Re-
fer to
Table 11-5 for the interpretation of this field.
11.5.2
PLL_RATIOS Register
The PLL_RATIOS register controls the operation of the
separate memory-interface and CPU PLLs. Fields in this
register determine if the PLLs are active and what in-
put:output ratio each PLL should generate.
Table 11-6the PLLs are connected and how fields in the
PLL_RATIOS register control them.
CR (CPU-to-memory PLL Ratio). The three-bit CR field
selects one of five input-to-output clock ratios for the
CPU PLL. The input clock is the memory system clock;
the output clock determines TM1100’s core operating
frequency. The default value is zero, which implies a 1:1
CPU:memory ratio. See
Table 11-6 for other encodings.
SR (Memory-to-external PLL Ratio). The one-bit SR
field selects one of two memory-to-external clock ratios
for the memory interface PLL. The PLL input is TM1100’s
external input clock TRI_CLKIN; the PLL output deter-
mines the operating frequency of the memory interface
and SDRAM devices. The default value is zero, which
implies a 2:1 memory:external ratio. A value of one im-
plies a 3:1 ratio.
CD (CPU PLL Disable). The one-bit CD field determines
whether or not the CPU PLL is turned on. The reset value
is one, which disables operation of the CPU PLL and dis-
sipates almost no power. For normal operation the value
should be zero, enabling the CPU PLL.
CB (CPU PLL Bypass). The one-bit CB field determines
whether the input or the output of the CPU PLL drives
Table 11-3. Example Memory Congurations
Size
(MB)
Ranks
Rank Congurations
Max.
MHz
Peak
MB/s
0.5
1
two 2
×64K×16 SDRAM
133
532
1
one 2
×128K×32 SGRAM
133
532
1two 2
×128K×16 SDRAM
133
532
2
1
one 2
×256K×32 SDRAM
133
532
4
1
two 2
×512K×16 SDRAM
133
532
8
1
four 2
×1M×8 SDRAM
133
532
2two 2
×512K×16 SDRAM
two 2
×512K×16 SDRAM
133
532
1
one 4
×512K×32 SDRAM
133
532
16
1
eight 2
×2M×4 SDRAM
66
264
2
one 4
×512K×32 SDRAM
one 4
×512K×32 SDRAM
133
532
24
3
one 4
×512K×32 SDRAM
one 4
×512K×32 SDRAM
one 4
×512K×32 SDRAM
125
500
32
2
eight 2
×2M×4 SDRAM
eight 2
×2M×4 SDRAM
50
200
4
one 4
×512K×32 SDRAM
one 4
×512K×32 SDRAM
one 4
×512K×32 SDRAM
one 4
×512K×32 SDRAM
100
400
64
4
eight 2
×2M×4 SDRAM
eight 2
×2M×4 SDRAM
eight 2
×2M×4 SDRAM
eight 2
×2M×4 SDRAM
50
(with
buffs.)
200
Table 11-4. Memory Interface Conguration
Registers
Register
Purpose
MM_CONFIG
Describes external memory conguration
PLL_RATIOS
Controls separate memory and CPU PLLs
(phase-locked loops)
Figure 11-2. Memory interface configuration registers.
31
0
MM_CONFIG (r/o)
42
3
SIZE
PLL_RATIOS (r/o)
CR
REFRESH
19
31
0
42
3
7
0
SDRAM PLL Bypass
SDRAM PLL Disable
CPU PLL Bypass
CPU PLL Disable
SDRAM Ratio
CPU Ratio
5
6
SB SD CB CD SR
0x10 0100
MMIO_base
offset:
0x10 0300