Philips Semiconductors
SDRAM Memory System
PRELIMINARY SPECIFICATION
12-5
tion Both PLLs must be activated, i.e. {CD,CB,SD,SB}
must be equal to 0000 (binary value).
The operating limits of the internal PLLs are:
27 MHz < Output of the SDRAM PLL < 200 MHz
33 MHz < Output of the CPU PLL < 266 MHz
These are not the speed grades of the chips, just the PLL
limits.
CR (CPU-to-memory PLL ratio).
The 3-bit CR field se-
lects one of five input-to-output clock ratios for the CPU
PLL. The input clock is the memory system clock; the
output clock determines the PNX1300 core operating fre-
quency. The default value is
‘
0
’
, which implies a 1:1
CPU:memory ratio. See
Table 12-8
for other encoding.
SR (Memory-to-external PLL ratio).
The 1-bit SR field
selects one of two memory-to-external clock ratios for
the memory interface PLL. The PLL input is PNX1300
’
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
‘
0
’
, which im-
plies a 2:1 memory:external ratio. A value of
‘
1
’
implies a
3:1 ratio.
CD (CPU PLL disable).
The 1-bit CD field determines
whether or not the CPU PLL is turned on. The reset value
is
‘
1
’
, 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 1-bit CB field determines
whether the input or the output of the CPU PLL drives
PNX1300
’
s core logic. The default value is
‘
1
’
, which
causes the PNX1300 core to be clocked by the input of
the CPU PLL (i.e., the memory interface clock). A value
of
‘
0
’
causes normal operation, and the core is clocked by
the output of the CPU PLL.
Note that if both CB and SB are set to
‘
1
’
(bypass the
CPU PLL and the SDRAM PLL), PNX1300
’
s core logic is
effectively clocked at the external input frequency.
Note: it is illegal to use the output of a disabled PLL. For
example, it is illegal to have CD set to
‘
1
’
while CB is set
to
‘
0
’
.
SD (SDRAM PLL disable).
The 1-bit SD field deter-
mines whether or not the SDRAM PLL is turned on. The
default value is
‘
1
’
, which disables the SDRAM PLL. In
this state, it dissipates almost no power. For normal op-
eration the value should be
‘
0
’
, enabling the SDRAM
PLL.
SB (SDRAM PLL bypass).
The 1-bit SB field deter-
mines whether the input or the output of the SDRAM PLL
drives the memory interface and memory devices. The
default value is
‘
1
’
, which causes the memory system to
be clocked by the input of the SDRAM PLL (PNX1300
’
s
external input clock). A value of
’
0
’
causes normal oper-
ation, and the memory system is clocked by the output of
the SDRAM PLL.
12.7
MEMORY INTERFACE PIN LIST
The memory interface consists of 61 signal pins includ-
ing clocks (but excluding power and ground pins).
Table 12-9
lists the interface signal pins.
12.8
ADDRESS MAPPING
The address mapping is determined by the state of the
rank-size bits and the bus width bit in the MM_CONFIG
register.
12.8.1
Address Mapping in 32-bit mode
Table 12-10
shows how internal address bits from the
PNX1300 data highway bus are mapped to main-memo-
ry address-bus and chip select pins (MM_A[13:0],
MM_CS#[3:0]) in 32-bit data bus mode.
The column
“
Rank Addr./H.Way Bits
”
specifies which in-
ternal data-highway address bits select the preliminary
SDRAM rank. The actual rank used is subject to the lim-
itation implied by the relationship between SDRAM aper-
ture size (described in
Section 13.2.1
) and the rank size.
Table 12-9. Memory Interface Signal Pins
Name
Function
I/O
Active...
MM_CLK[1:0]
MM_CS#[3..0]
Memory bus clock
Chip selects for the four
memory ranks or Address
Row-address strobe
Column address strobe
Write enable
Address
Clock enable
Byte enables for dq bus
Bi-directional data bus
O
O
High
Low
MM_RAS#
MM_CAS#
MM_WE#
MM_A[13:0]
MM_CKE[1:0]
MM_DQM[3:0]
MM_DQ[31:0]
O
O
O
O
O
O
I/O
Low
Low
Low
High
High
High
High
Table 12-10. 32-bit Address Mapping
Rank
Size
Rank
Addr.
Row
Address
Column
Address
Bank
Address
H.Way
Bits
Pins
H.Way
Bits
Pins
H.Way
Bits
PinHBit
4 MB
23
–
22
10
–
0
21
–
11
7
–
0
10
–
6,
4
–
2
11,
11
–
6,
4
–
2
11,
12
–
6,
4
–
2
25,
24,
11,
12
–
6,
4
–
2
11
5
8 MB
24-23
12,
10
–
0
11,
22
–
12
12,
8
–
0
11
16 MB
25-24
13-12
10
–
0
12-11,
23
–
13
12,
9
–
0
11
32 MB
–
CS#3
CS#2
13-12
10
–
0
25,
24,
12-11,
23
–
13
CS#3,
CS#2,
12
9
–
0
11