User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 6: DRAM Page
123
S
UPPORTED
DRAM
S
AND
DIMM
S
DDR SDRAMS
The memory controller supports standard JEDEC DDR SDRAMs in x8 and x16 configurations, and also the
x32 DDR SGRAMs. In addition the FCRAMs are supported in both x8 and x16 configurations. The x32 SGRAM
parts only use one DQS signal to cover all 32 data bits, the DQS from the DRAM should be connected to the
corresponding four DQS pins on the controller (M_DQS[7:4] for the upper word and M_DQS[3:0] for the lower
word); the controller will only drive on one of the lines but needs to receive on all of them. X4 configuration
parts are not supported since the interface has insufficient DQS signals.
If the memory channel is configured for SGRAMs the A10 and A8 signals may need to be swapped. The
memory controller follows the DDR standard and puts the AutoPrecharge flag on the A10 address bit, but many
SGRAMs need it on A8. (In parts with system revision indicating PERIPH_REV3 or greater the pre_on_A8 bit
can be set in the
mc_drammode
register to cause the controller to put the AutoPrecharge flag on A8 instead
of A10.)
Non-standard 8 bank DDR SDRAMs use A[12] as the third bank address bit, 8 bank FCRAMS use A[14] as
the third bank address bit. This is enabled if three bits are set in the bank address selection register. For regular
SDRAMS if the ram_with_A13 bit is set in the
mc_drammode
register the BA[2] is brought out on the A13 pin
and A12 reverts to being a row address.
DDR FCRAMs
Memory channels can be configured to use FCRAMs. These require two extra row address bits and use a
function (FN) flag to distinguish between a read and write access. The JEDEC defined footprint for standard
DDR and FCRAM parts are identical with the exception of pins 21, 22, and 23. On a DDR SDRAM these pins
are WE#, CAS#, and RAS#, respectively. On the FCRAM, they become A14, A13, and FN (effectively WE#).
The BCM1250 or BCM1125/H uses the same mapping when a channel is configured for FCRAM use, so:
•
Mn_WE_L becomes Mn_A[14] for FCRAM.
•
Mn_CAS_L becomes Mn_A[13] for FCRAM.
•
Mn_RAS_L becomes Mn_FN for FCRAM.
•
Mn_CKE is called Mn_PD_L but is the same.
This allows the standard footprint to be used and either type of memory populated. The FCRAM parts generally
have a CAS to write data latency that is one less than the CAS latency, this is supported by setting the tCwD
parameter in the SDRAM timing register.
Table 68: Supported SDRAMs
DDR SDRAMs
Technology
Size (row x col)
Size (row x col)
JEDEC std (4 bank)
64 Mb
8Mx8 (4k x 512)
4Mx16 (4k x 256)
128 Mb
16Mx8 (4k x 1k)
8Mx16 (4k x 512)
256 Mb
32Mx8 (8k x 1k)
16Mx16 (8k x 512)
Non-std (8 bank)
64 Mb
2Mx32
128 Mb
4Mx32
256 Mb
8Mx32
FCRAM (4 bank)
256 Mb
32Mx8(32k x 256)
16Mx16(32k x 128)