Datasheet

Chapter 11. Synchronous/Asynchronous DRAM Controller Module 11-15
Asynchronous Operation
Figure 11-10. Write Hit in Continuous Page Mode
11.3.3.4 Extended Data Out (EDO) Operation
EDO is a variation of page mode that allows the DRAM to continue driving data out of the
device while CAS
is precharging. To support EDO DRAMs, the DRAM controller delays
internal termination of the cycle by one clock so data can continue to be captured as CAS
is being precharged. For data to be driven by the DRAMs, RAS is held after CAS is
negated. EDO operation does not affect write operations. EDO DRAMs can be used in
continuous page or burst page modes. Single accesses not followed by a hit in the page look
like non-page-mode accesses.
Figure 11-11 shows four consecutive EDO accesses. Note that data is sampled after CAS
is negated and that on the last page access, CAS is held until after data is sampled to assure
that the data is driven. This allows RAS
to be precharged before the end of the cycle.
Figure 11-11. EDO Read Operation (3-2-2-2)
A[31:0]
RAS[1] or [0]
CAS
[3:0]
DRAMW
D[31:0]
RCD = 0
CAS = 01
Bus Cycle 1 Bus Cycle 2
Page Hit
Page Miss
Row Column Column
CLKIN
A[31:0]
RAS[1] or [0]
CAS[3:0]
DRAMW
D[31:0]
RCD = 0
CAS = 00
CLKIN