IC41C16256
IC41LV16256
FunctionalDescription
Refresh Cycle
The IC41C16256 and IC41LV16256 is a CMOS DRAM
optimized for high-speed bandwidth, low power applica-
tions. During READ or WRITE cycles, each bit is uniquely
addressed through the 18 address bits. These are en-
tered 9 bits (A0-A8) at a time. The row address is latched
by the Row Address Strobe (RAS). The column address
is latched by the Column Address Strobe (CAS) .
To retain data, 512 refresh cycles are required in each
8 ms period. There are two ways to refresh the memory.
1. By clocking each of the 512 row addresses (A0 through
A8) with RAS at least once every 8 ms. Any read, write,
read-modify-write or RAS-only cycle refreshes 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 9-bit counter provides the row ad-
dresses and the external address inputs are ignored.
The IC41C16256 and IC41LV16256 has two CAS controls,
LCAS and UCAS. The LCAS and UCAS inputs internally
generates a CAS signal functioning in an identical man-
ner to the single CAS input on the other 256K x 16
DRAMs. The key difference is that each CAS controls its
corresponding I/O tristate logic (in conjunction with OE
and WE and RAS). LCAS controls I/O0 through I/O7 and
UCAS controls I/O8 through I/O15.
The IC41C16256 and IC41LV16256 CAS function is
determined by the first CAS (LCAS or UCAS) transitioning
LOW and the last transitioning back HIGH. The two CAS
controls give the IC41C16256 both BYTE READ and
BYTE WRITE cycle capabilities.
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.
Extended Data Out Page Mode
EDO page mode operation permits all 512 columns within
a selected row to be randomly accessed at a high data
rate.
In EDO page mode read cycle, the data-out is held to the
next CAS cycle’s falling edge, instead of the rising edge.
For this reason, the valid data output time in EDO page
mode is extended compared with the fast page mode. In
the fast page mode, the valid data output time becomes
shorter as the CAS cycle time becomes shorter. Therefore,
in EDO page mode, the timing margin in read cycle is
larger than that of the fast page mode even if the CAS cycle
time becomes shorter.
In EDO page mode, due to the extended data function, the
CAS cycle time can be shorter than in the fast page mode
if the timing margin is the same.
The EDO page mode allows both read and write opera-
tions during one RAS cycle, but the performance is
equivalent to that of the fast page mode in that case.
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.
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.
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).
Write Cycle
During power-on, it is recommended that RAS track with
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 first.
VCC or be held at a valid VIH to avoid current surges.
Integrated Circuit Solution Inc.
5
DR018-0C 04/23/2004
ISSI [ INTEGRATED SILICON SOLUTION, INC ]
