AS4C64M8D2
Burst read with auto precharge
If A10 is HIGH when a Read Command is issued, the Read with Auto-Precharge function is engaged. The DDR2
SDRAM starts an Auto-Precharge operation on the rising edge which is (AL + BL/2) cycles later from the Read
with AP command if tRAS(min) and tRTP are satisfied. If tRAS(min) is not satisfied at the edge, the start point of Auto-
Precharge operation will be delayed until tRAS(min) is satisfied. If tRTP(min) is not satisfied at the edge, the start
point of Auto-precharge operation will be delayed until tRTP(min) is satisfied.
In case the internal precharge is pushed out by tRTP, tRP starts at the point where the internal precharge happens
(not at the next rising clock edge after this event). So for BL = 4 the minimum time from Read with Auto-
Precharge to the next Activate command becomes AL + tRTP + tRP. For BL = 8 the time from Read with Auto-
Precharge to the next Activate command is AL + 2 + tRTP + tRP. Note that both parameters tRTP and tRP have to be
rounded up to the next integer value. In any event internal precharge does not start earlier than two clocks after
the last 4-bit prefetch.
A new bank active (command) may be issued to the same bank if the following two conditions are satisfied
simultaneously:
(1) The RAS# precharge time (tRP) has been satisfied from the clock at which the Auto-Precharge begins.
(2) The RAS# cycle time (tRC) from the previous bank activation has been satisfied.
Burst write with auto precharge
If A10 is HIGH when a Write Command is issued, the Write with Auto-Precharge function is engaged. The DDR2
SDRAM automatically begins precharge operation after the completion of the burst write plus Write recovery time
(tWR). The bank undergoing auto-precharge from the completion of the write burst may be reactivated if the
following two conditions are satisfied.
(1) The data-in to bank activate delay time (WR + tRP) has been satisfied.
(2) The RAS# cycle time (tRC) from the previous bank activation has been satisfied.
Table 12. Precharge & Auto Precharge Clarification
Minimum Delay between “From
Command” to “To Command”
From Command
Read
To Command
Unit Note
tCK 1,2
tCK 1,2
Precharge (to same Bank as Read)
Precharge All
Precharge (to same Bank as Read w/AP)
Precharge All
Precharge (to same Bank as Write)
Precharge All
Precharge (to same Bank as Write w/AP)
Precharge All
AL+BL/2+max(RTP,2)-2
AL+BL/2+max(RTP,2)-2
AL+BL/2+max(RTP,2)-2
AL+BL/2+max(RTP,2)-2
Read w/AP
Write
WL+BL/2+tWR
WL+BL/2+tWR
WL+BL/2+tWR
WL+BL/2+tWR
tCK
tCK
tCK
tCK
2
2
2
2
Write w/AP
Precharge
Precharge All
Precharge (to same Bank as Precharge)
Precharge All
1
1
1
1
Precharge
Precharge All
NOTE 1: RTP [cycles] =RU {tRTP [ns]/tCK (avg) [ns]}, where RU stands for round up.
NOTE 2: For a given bank, the precharge period should be counted from the latest precharge command, either
one bank precharge or precharge all, issued to that bank.The precharge period is satisfied after tRP or tRPall(=tRP
for 4 bank device) depending on the latest precharge command issued to that bank.
Confidential
17
Rev. 1.0
Feb. /2014
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
