BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
138
Section 6: DRAM
Document
1250_1125-UM100CB-R
Table 74: Memory Clock Configuration Register
mc_clock_cfg_0 -
00_1005_1500
mc_clock_cfg_1 -
00_1005_2500
Bits
Name
Default
Description
3:0
clk_ratio
4’h4
ZBclk/mclk ratio Mclk when ZBclk=400 MHz
0100 2x
200
0101 2.5x
160
0110 3x
133
0111 3.5x
114
1000 4x
100
1001 4.5x
88
Others Reserved
7:4
cs_absence
4’h0
On parts with system_revision
≥
PERIPH_REV3 setting these bits will disable the
refresh cycle for the corresponding chip select. On earlier revisions all chip selects will
always be refreshed.
15:8
ref_rate
8’hC4
Refresh Rate: (value+1) x 16 MCLK
examples are:
8'h62
99(x16) MCLK cycles at 100MHz (15.84us).
8'h81
130(x16) MCLK cycles at 133MHz (15.64us).
8'hc4
197(x16) MCLK cycles at 200MHz (15.76us).
Note that the controller will refresh one chip select at a time (to save the power spike
of all the SDRAMs refreshing simultaneously) so refresh cycles will be seen on the
channel four times as often as this field implies (in large memory mode two chip selects
are refreshed at a time).
18:16
clock_drive
3’b111
This sets the drive strength (and therefore slew rate) of the output drivers for the clocks.
0 gives the weakest drive (slowest slew rate) and 7 the hardest. See
.
19
clock_class
1’b1
This bit should be clear to have the clock drivers configured for SSTL_2 Class 1
operation, and set for SSTL_2 class 2.
22:20
data_drive
3’b0
This sets the drive strength (and therefore slew rate) of the output drivers for the data
lines. 0 gives the weakest drive (slowest slew rate) and 7 the hardest. See
23
data_class
1’b0
This bit should be clear to have the data drivers configured for SSTL_2 Class 1
operation, and set for SSTL_2 class 2.
26:24
addr_drive
3’b0
This sets the drive strength (and therefore slew rate) of the output drivers for the
address and control lines. 0 gives the weakest drive (slowest slew rate) and 7 the
hardest. See
Section: “I/O Control” on page 128
27
addr_class
1’b0
This bit should be clear to have the address and control drivers configured for SSTL_2
Class 1 operation, and set for SSTL_2 class 2.
29:28
reserved
2’b0
Reserved
30
ref_disable
1’b0
On BCM1250 prior to PERIPH_REV3: Reserved
On other parts: If this bit is set refresh cycles are disabled. This can be useful during
debugging, but must not be set in normal operation.
31
dll_bypass
1’b0
Set this bit to bypass the DLLs. This should not be set in normal operation.
35:32
dqi_skew
4’b1000
DQS to data input skew control. See
Section: “I/O Control” on page 128
39:36
reserved
4’b0
Reserved
43:40
dqo_skew
4’b1000
DQS to data output skew control. See
Section: “I/O Control” on page 128
47:44
reserved
4’b0
Reserved
51:48
addr_skew
4’b1000
Address/control output delay from rising memory clock. See
.
55:52
reserved
4’b0
Reserved
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