IDT DDR Controller
DDR Write Transaction
79RC32438 User Reference Manual
7 - 22
November 4, 2002
Notes
Figure 7.18 DDR SDRAM Write Transaction with Wrong Page Active in Bank (Bank Page Miss)
1
A DDR SDRAM write transaction in which the wrong page is active in a bank is shown in Figure 7.18. If
no pages had been active, then the transaction would have started with the ACTIVE command (i.e., step
three below). If the correct page had been active (bank page hit), then the transaction would have started
with the WRITE command (i.e., step five below). A DDR SDRAM write transaction in which the wrong page
is active consists of the following steps.
1. The RC32438 asserts the appropriate DDR SDRAM chip select (DDRCSNx), drives the bank select
pins (DDRBA[1:0]) with the value of the bank to be precharged, drives the AP address bit low (see
Tables 7.3 and 7.4) to indicate that only that bank is to be precharged, and drives the PRECHARGE
command (see Table 7.5) on the rising edge of DDRCKPx. This indicates the start of a transaction.
2. One clock cycle after step #1, the RC32438 drives the NOP command (see Table 7.5).
3. RP clock cycles after step #1, the RC32438 drives the bank select pins (DDRBA[1:0]) with the value
of the bank to be accessed, drives the address bus (DDRADDR[13:0]) with the DDR SDRAM row
address, and drives the ACTIVE command (see Table 7.5) on the rising edge of DDRCKPx. Note
that step #2 is skipped if the value of RP = 1 (see DDRC Register).
4. One clock cycle after step one, the RC32438 drives the NOP command (see Table 7.5).
5. RCD clock cycles after step #3, the RC32438 drives the address bus (DDRADDR[13:0]) with the
DDR SDRAM column address, and drives the WRITE command (see Table 7.5). At this time the
RC32438 may also assert the appropriate buffer output enables (DDROEN[3:0]) if the DBM bit in
the DDRC register is set. Note that step #4 is skipped if the value of RCD = 1 (see DDRC register).
6. One clock cycle after step #5, the RC32438 may drive the NOP or WRITE command depending on
the amount of data to be written. Figure 7.18 shows a write of four words, and thus two write
commands are issued (each write command writes a pair of data). During the last write command
issued, the RC32438 may assert the auto-precharge (AP) bit of the address bus (see Tables 7.3 and
7.4) depending on the state of the AP field in the DDRC register.
1.
The programmable parameters shown in Figure 7.18 are for illustrative purposes only and may vary.
RP = 2
RCD = 2
WR = 3
ATP = 8
Row A
Col A0
Col A2
NOP
PRECHG NOP
ACTV
NOP
WR
WR
NOP
NOP
NOP
NOP
PRECHG NOP
BNKx
BNKx
BNKx
BNKx
BNKx
FF
DM0 DM1DM2DM3
FF
D0
D1 D2
D3
DDRCKPx
DDRCKNx
DDRCSNx
DDRADDR[13:0]
DDRCMD
DDRCKE
DDRBA[1:0]
DDR
OEN[3:0]
DDRDM[7:0]
DDRDQSx
DDRDATA[Y:0]
WRITE TRANSACTION
Transaction
NEXT TRANSACTION