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IDT DDR Controller
Example of DDR SDRAM Initialization
79RC32438 User Reference Manual
7 - 25
November 4, 2002
Notes
Figure 7.20 DDR SDRAM Custom Transaction
A DDR SDRAM Custom transaction is shown in Figure 7.20 and consists of the following steps.
1. The CPU configures the programmable parameters in the DDRCUST register for the desired DDR
SDRAM custom transaction.
2. The CPU performs a write operation to DDR SDRAM space. This causes the RC32438 to assert the
chip selects (DDRCSNx) programmed in the CS field of the DDRCUST register, drive the address
bus (DDRADDR[13:0]) with the CPU address bits [15:2], drive the bank select pins (DDRBA[1:0])
with the value programmed in the BA field of the DDRCUST register, drive the DDRCKE pin with the
value programmed in the CKE field of the DDRCUST register, and drive the DDR SDRAM custom
command programmed in the RAS, CAS, and WE fields of the DDRCUST register. Note that the
DDRDM[7:0] and DDROEN[3:0] pins are automatically negated during custom transactions, and
that the DDRDATA[31:0] and DDRDQS[3:0] pins are not driven.
3. One clock cycle after step #2, the RC32438 negates all of the asserted chip selects and clears the
address and bank select pins. The DDR SDRAM custom command programmed in the DDRCUST
register continues to be driven until the next DDR transaction. At this point the transaction is
completed and a new transaction may begin.
4. Note that step #2 must be a write operation to DDR SDRAM space. Still, the write data for this oper-
ation is meaningless. Only the address bits [15:2] of the transaction are meaningful as they are
driven onto the DDRADDR[13:0] pins.
Example of DDR SDRAM Initialization
The IDT79EB438 board uses two Micron MT46V16M16 (4 Meg x 16 x 4 banks) DDR SDRAM devices
tied to DDRCSN[0].
The specifics of this DDR SDRAM devices are listed below:
a). Configuration
: 4 MB x 16 x 4 banks
b). Refresh Count
: 8 K
c). Row Addressing
: 8 K (A0-A12)
d). Bank Addressing
: 4 ( BA0, BA1)
e). Column Addressing
: 512 (A0-A8)
A[15:2]
NOP
NOP
NOP
Custom
Custom
Custom
Custom
Custom Custom Custom
Custom
ACTV
NOP
Custom
BNKx
DDRCKPx
DDRCKNx
DDRCSNx
DDRADDR[13:0]
DDRCMD
DDRCKE
DDRBA[1:0]
DDRDM[7:0]
DDR
OEN[3:0]
DDRDQS[3:0]
DDRDATA[31:0]
Transaction
CUSTOM TRANS
NEXT TRANSACTION