IC41C82002S
IC41LV82002S
FunctionalDescription
Refresh Cycle
The IC41C82002S and IC41LV82002S are CMOS DRAMs
optimized for high-speed bandwidth, low power
applications. During READ or WRITE cycles, each bit is
uniquely addressed through the 11 address bits. These
are entered 11 bits (A0-A10) at a time for the 2K refresh
device. The row address is latched by the Row Address
Strobe (RAS). The column address is latched by the
Column Address Strobe (CAS). RAS is used to latch the
first 11 bits and CAS is used to latch the latter ten bits.
To retain data, 2,048 refresh cycles are required in each
32 ms period. There are two ways to refresh the memory:
1. By clocking each of the 2,048 row addresses (A0
through A10) with RAS at least once every 32 ms. Any
read, write, read-modify-write or RAS-only cycle re-
freshes the addressed row.
2. Using a CAS-before-RAS refresh cycle. CAS-before-
RAS refresh is activated by the falling edge of RAS,
while holding CAS LOW. In CAS-before-RAS refresh
cycle, an internal 11-bit counter provides the row ad-
dresses and the external address inputs are ignored.
Memory Cycle
A memory cycle is initiated by bring RAS LOW and it is
terminated by returning both RAS and CAS HIGH. To
ensures proper device operation and data integrity any
memory cycle, once initiated, must not be ended or
aborted before the minimum tRAS time has expired. A new
cycle must not be initiated until the minimum precharge
time tRP, tCP has elapsed.
CAS-before-RAS is a refresh-only mode and no data
access or device selection is allowed. Thus, the output
remains in the High-Z state during the cycle.
Self Refresh Cycle
The Self Refresh allows the user a dynamic refresh, data
retention mode at the extended refresh period of 64 ms.
i.e., 31.25 µs per row when using distributed CBR refreshes.
The feature also allows the user the choice of a fully static,
low power data retention mode. The optional Self Refresh
feature is initiated by performing a CBR Refresh cycle and
holding RAS LOW for the specified tRASS.
Read Cycle
A read cycle is initiated by the falling edge of CAS or OE,
whichever occurs last, while holding WE HIGH. The
column address must be held for a minimum time specified
by tAR. Data Out becomes valid only when tRAC, tAA, tCAC
and tOE are all satisfied. As a result, the access time is
dependent on the timing relationships between these
parameters.
The Self Refresh mode is terminated by driving RAS
HIGH for a minimum time of tRP. This delay allows for the
completion of any internal refresh cycles that may be in
process at the time of the RAS LOW-to-HIGH transition.
If the DRAM controller uses a distributed refresh sequence,
a burst refresh is not required upon exiting Self Refresh.
Write Cycle
A write cycle is initiated by the falling edge of CAS and WE,
whichever occurs last. The input data must be valid at or
before the falling edge of CAS or WE, whichever occurs
last.
However, if the DRAM controller utilizes a RAS-only or
burst refresh sequence, all 2,048 rows must be refreshed
within the average internal refresh rate, prior to the
resumption of normal operation.
Power-On
After application of the VCC supply, an initial pause of
200 µs is required followed by a minimum of eight initial-
ization cycles (any combination of cycles containing a
RAS signal).
During power-on, it is recommended that RAS track with
VCC or be held at a valid VIH to avoid current surges.
4
Integrated Circuit Solution Inc.
DR022-0A 08/20/2001
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
