參數(shù)資料
型號(hào): μPD481850
廠商: NEC Corp.
英文描述: Synchronous Graphics Memory (SGRAM)(8M 同步圖形存儲(chǔ)器)
中文描述: 同步圖形存儲(chǔ)器(SGRAM)(8分同步圖形存儲(chǔ)器)
文件頁(yè)數(shù): 30/94頁(yè)
文件大?。?/td> 1180K
代理商: ΜPD481850
Preliminary Data Sheet
30
μ
PD481850 for Rev.L
10. Precharge
The precharge command can be asserted anytime after t
RAS(MIN.)
is satisfied.
Soon after the precharge command is asserted, precharge operation performed and the synchronous GRAM
enters the idle state after t
RP
is satisfied. The parameter t
RP
is the time required to perform the precharge.
The earliest timing in a read cycle that a precharge command can be asserted without losing any data in the burst
is as follows.
/CAS latency = 2 or 3 : One clock earlier than the last read data.
T0
T1
T2
T3
T4
T5
T6
T7
Burst length=4
READ
READ
Q1
Q2
Q3
Q4
PRE
Hi-Z
Q1
Q2
Q3
Q4
PRE
Hi-Z
(t
RAS
is satisfied)
CLK
Command
/CAS latency = 2
DQ
Command
/CAS latency = 3
DQ
In order to write all data to the memory cell correctly, the asynchronous parameter “t
DPL
” must be satisfied. The
t
DPL(MIN.)
specification defines the earliest time that a precharge command can be asserted. Minimum number of
clocks are calculated by dividing t
DPL (MIN.)
with clock cycle time.
In summary, the precharge command can be asserted relative to 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
Read
Write
2
–1
+t
DPL(MIN.)
3
–1
+t
DPL(MIN.)
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