VG36644041DT / VG36648041DT / VG36641641DT
CMOS Synchronous Dynamic RAM
VIS
7.Precharge
The precharge command can be asserted anytime after t
is satisfied.
RAS(min.)
Soon after the precharge command is asserted, the precharge operation is performed and the synchronous DRAM enters the
idle state after t is satisfied. The parameter t is the time required to perform the precharge.
RP(min.)
RP
The earliest timing in a read cycle that a precharge command can be asserted without losing any data in the burst is as follows.
PrechargeE
Burst lengh=4
T0
T1
T3
T6
T2
T4
T5
T7
CLK
Command
Read
PRE
Q2
CAS latency = 2
Hi - Z
DQ
Q0
Q1
Q3
Command
CAS latency = 3
DQ
Read
PRE
Q1
Hi - Z
Q3
Q2
Q0
(tRAS is satisfied)
In order to write all data to the memory cell correctly, the asynchronous parameter ”tDPL” must be satisfied. The
tDPL(min.) specification defines the earliest time that a precharge command can be asserted. The minimum number of
clocks can be calculated by dividing tDPL(min.) with the clock cycle time.
In summary, the precharge command can be asserted relative to the reference clock that indicates the last data word is
valid. In the following table, minus means clocks before the reference; plus means time after the reference.
CAS latency
2
Read
-1
Write
+ tDPL(min.)
3
-2
+ tDPL(min.)
Document :1G5-0177
Rev.2
Page19
VML [ VANGUARD INTERNATIONAL SEMICONDUCTOR ]
