V53C8258H
MOSEL VITELIC
controlled Write Cycle, when the leading edge of
WE occurs prior to the CAS low transition, the I/O
data pins will be in the High-Z state at the beginning
of the Write function. Ending the Write with RAS or
CAS will maintain the output in the High-Z state.
In the WE controlled Write Cycle, OE must be in
the high state and tOED must be satisfied.
Functional Description
The V53C8258H is a CMOS dynamic RAM
optimized for high data bandwidth, low power
applications. It is functionally similar to a traditional
dynamic RAM. The V53C8258H reads and writes
data by multiplexing an 18-bit address into a 9-bit
row and a 9-bit column address. The row address is
latched by the Row Address Strobe (RAS). The
column address “flows through” an internal address
buffer and is latched by the Column Address Strobe
(CAS). Because access time is primarily dependent
on a valid column address rather than the precise
time that the CAS edge occurs, the delay time from
RAS to CAS has little effect on the access time.
Extended Data Output Page Mode
EDO Page operation permits all 512 columns
within a selected row of the device to be randomly
accessed at a high data rate. Maintaining RAS low
while performing successive CAS cycles retains the
row address internally and eliminates the need to
reapply it for each cycle. The column address buffer
acts as a transparent or flow-through latch while
CAS is high. Thus, access begins from the
occurrence of a valid column address rather than
from the falling edge of CAS, eliminating tASC and tT
from the critical timing path. CAS latches the
address into the column address buffer. During
EDO operation, Read, Write, Read-Modify-Write or
Read-Write-Read cycles are possible at random
addresses within a row. Following the initial entry
cycle into Hyper Page Mode, access is tCAA or tCAP
controlled. If the column address is valid prior to the
rising edge of CAS, the access time is referenced to
the CAS rising edge and is specified by tCAP. If the
column address is valid after the rising CAS edge,
access is timed from the occurrence of a valid
address and is specified by tCAA. In both cases, the
falling edge of CAS latches the address and
enables the output.
Memory Cycle
A memory cycle is initiated by bringing RAS low.
Any memory cycle, once initiated, must not be
ended or aborted before the minimum tRAS time has
expired. This ensures proper device operation and
data integrity. A new cycle must not be initiated until
the minimum precharge time tRP/tCP has elapsed.
Read Cycle
A Read cycle is performed by holding the Write
Enable (WE) signal High during a RAS/CAS
operation. The column address must be held for a
minimum specified by tAR. Data Out becomes valid
only when tOAC, tRAC, tCAA and tCAC are all satisifed.
As a result, the access time is dependent on the
timing relationships between these parameters. For
example, the access time is limited by tCAA when
tRAC, tCAC and tOAC are all satisfied.
EDO provides a sustained data rate of 71 MHz for
applications that require high bandwidth such as
bit-mapped graphics or high-speed signal
processing. The following equation can be used to
calculate the maximum data rate:
Write Cycle
A Write Cycle is performed by taking WE and
CAS low during a RAS operation. The column
address is latched by CAS. The Write Cycle can be
WE controlled or CAS controlled depending on
whether WE or CAS falls later. Consequently, the
input data must be valid at or before the falling edge
of WE or CAS, whichever occurs last. In the CAS-
512
Data Rate =
tRC + 511 x tPC
V53C8258H Rev. 1.4 February 1997
15
MOSEL [ MOSEL VITELIC, CORP ]
