EtronTech
EM68916CWQA
z 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.
z 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 14.Precharge &Auto Precharge Clariification
Minimum Delay between “From
Command” to “To Command”
From Command
Read
To Command
Unit Notes
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
tCK
tCK
1,2
1,2
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
Write w/AP
Precharge
Precharge All
2
Precharge (to same Bank as Precharge)
Precharge All
1
1
1
1
2
Precharge
Precharge All
2
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 prechrage period is satisfied after tRP or tRPall(=tRP
for 4 bank device) depending on the latest precharge command issued to that bank.
Etron Confidential
19
Rev. 1.1
Apr. 2009
ETRON [ ETRON TECHNOLOGY, INC. ]
