IDT DDR Controller
DDR Custom Transaction
79RC32438 User Reference Manual
7 - 24
November 4, 2002
Notes
A DDR SDRAM refresh transaction is queued for execution whenever the DDR Refresh Timer expires
and the refresh enable bit (RE) in the DDRC register is set. If no active pages exists in any of the DDR
SDRAM banks, then the refresh transaction simply consists of an auto refresh command followed by RFC
clock cycles (i.e., the transaction starts with step three below). If there exists an active page in any of the
DDR SDRAMs, then a precharge-all command is first issued to deactivate all banks in all of the DDRs. This
is then followed by an auto-refresh command followed by RFC clock cycles. A DDR SDRAM refresh trans-
action with active pages is shown in Figure 7.19 and consists of the following steps.
1. The RC32438 asserts both DDR SDRAM chip selects (DDRCSN[1:0]), drives the AP address bit
high (see Tables 7.3 and 7.4) to indicate that all banks are 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 AUTO-REFRESH command (see Table 7.5).
Note that step two is skipped if the value of RP = 1 (see DDRC register).
4. One clock cycle after step #3, the RC32438 drives the NOP command (see Table 7.5).
5. RFC clock cycles after step #4, the RC32438 negates the DDR SDRAM chip selects
(DDRCSN[1:0]), the transaction is completed, and a new transaction may begin.
DDR Custom Transaction
This section describes the SDRAM custom transaction. The transaction involves seven programmable
parameters:
DDR Chip Select (
CS
). CS may be programmed to select DDRCSN[0], DDRDCSN[1] or both
DDR Write Enable Status (
WE
). WE specifies the state of the DDRWEN pin during a DDR custom
transaction
DDR RAS Status (
RAS
). RAS specifies the state of the DDRRASN pin during a DDR custom trans-
action
DDR CAS Status (
CAS
). CAS specifies the state of the DDRCASN signal during a DDR custom
transaction
DDR Clock Enable Status (
CKE
). CKE specifies the state of the DDRCKE signal during a DDR cus-
tom transaction.
DDR Bank Address Status (
BA
). BA specifies the state of the DDRBA[1:0] signals during a DDR
custom transaction.
DDR Auto Precharge Enable (
AP
). AP specifies the state of the auto precharge address bit during
a DDR custom transaction.