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
140
Section 6: DRAM
Document
1250_1125-UM100CB-R
34:32
dram_type
3’b0
DRAM type:
000: JEDEC DDR (one DQS for every 8 DQ bits)
001: FCRAM
010: DDR SGRAM (one DQS for every 32 DQ bits)
Others Reserved
35
large_mem
1’b0
If this bit is set large memory support (using an external chip select decoder) is enabled.
See
Section: “Larger Memory Systems” on page 124
36
pre_on_A8
1’b0
If this bit is set the AutoPrecharge flag will be output on the A8 address bit rather than
A10. (Only supported on parts with system revision PERIPH_REV3 or greater).
37
ram_with_A13
1’b0
This bit should be set when the large_mem bit is set if the row address uses A13. It
causes the CS[3:2] to be driven from bits [15:14] of the row address mask. It also needs
to be set to cause BA[2] to be output on A13 rather than A12 for non-standard 8 bank
DRAMs. (Only supported on parts with system revision PERIPH_REV3 or greater).
63:38
reserved
26’b0
Reserved
Table 76: DRAM Mode Register
(Cont.)
mc_drammode_0 -
00_1005_1140
mc_drammode_1 -
00_1005_2140
Bits
Name
Default
Description
Table 77: SDRAM Timing Register
mc_timing1_0 -
00_1005_1160
mc_timing1_1 -
00_1005_2160
Bits
Name
Range
Default
Description
3:0
tRCD
1-6
4’h3
RAS to CAS delay. This should be set to 1 for FCRAMs.
6:4
tCrD
1-6
3’h2
Cycles from CAS(read) to data (the CAS latency).
7
tCrDh
0-1
1’b0
If this bit is set the data capture is delayed by a half cycle from the integer part
of the CAS latency set in tCrD. See the discussion in
11:8
tCwD
1-2 or
1-4
4’h1
Delay from CAS to Write data.
On parts with system revision PERIPH_REV3 or greater the range is extended
to 1-4.
15:12
reserved
0
4’h0
Reserved
19:16
tRP
1-4
4’h4
Cycles required from PRECHARGE to RAS.
23:20
tRRD
1-4
4’h2
Cycles required from RAS to RAS for a different bank.
27:24
tRCw-1
1-15
4’ha
One less than cycles required from RAS(write) to next RAS of the same bank.
31:28
tRCr-1
1-15
4’h9
One less than cycles required from RAS(read) to next RAS of the same bank.
35:32
reserved
0
4’h0
Reserved
39:36
reserved
0
4’h0
Reserved
43:40
tCwCr
0-15
4’h4
Cycles of separation from write to read.
This field is calculated as: tCwCr = tRCw - (tRCD + tCwD + 2 + tWTR)
Note that tRCw is one greater than the value set in tRCw-1 field and tWTR is
the internal write to read delay for the SDRAM (normally specified as 1 cycle).
47:44
reserved
0
4’h0
Reserved
51:48
reserved
0
4’h0
Reserved
55:52
tRFC
0-15
4’hc
Cycles required from Auto-refresh to Active or Auto-refresh.
59:56
tFIFO
0-1
4’h1
Additional cycles required for data capture FIFO.