8 MEG x 8
FPM DRAM
GENERAL DESCRIPTION (continued)
RAS# signal, then the column address by CAS#. Both
devices provide FAST-PAGE-MODE operation, allow-
ing for fast successive data operations (READ, WRITE,
or READ-MODIFY-WRITE) within a given row.
The MT4LC8M8E1 and MT4LC8M8B6 must be re-
freshed periodically in order to retain stored data.
the MT4LC8M8B6 refreshes one row for every CBR
cycle. So with either device, executing 4,096 CBR cycles
covers all rows. The CBR REFRESH cycle will invoke the
internal refresh counter for automatic RAS# address-
ing. Alternatively, RAS#-ONLY REFRESH capability is
inherently provided. However, with this method only
one row is refreshed at a time; so for the MT4LC8M8E1,
8,192 RAS#-ONLY REFRESH cycles must be executed
every 64ms to cover all rows. Some compatibility issues
may become apparent. JEDEC strongly recommends
the use of CBR REFRESH for this device.
An optional self refresh mode is also available on the
“S” version. The self refresh feature is initiated by
performing a CBR REFRESH cycle and holding RAS#
LOW for the specified
t
RASS. The “S” option allows for
an extended refresh period of 128ms, or 31.25µs per
row for a 4K refresh and 15.625µs per row for an 8K
refresh when using a distributed CBR REFRESH. This
refresh rate can be applied during normal operation, as
well as during a standby or battery backup mode.
The self refresh mode is terminated by driving RAS#
HIGH for a minimum time of
t
RPS. 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
CBR refresh sequence, a burst refresh is not required
upon exiting self refresh. However, if the DRAM con-
troller utilizes RAS#-ONLY or burst CBR refresh se-
quence, all rows must be refreshed with a refresh rate of
t
RC minimum prior to the resumption of normal
operation.
FAST PAGE MODE ACCESS
Each location in the DRAM is uniquely addressable
as mentioned in the General Description. The data for
each location is accessed via the eight I/O pins (DQ0-
DQ7). The WE# signal must be activated to execute a
WRITE operation; otherwise, a READ operation will be
performed. The OE# signal must be activated to enable
the DQ output drivers for a read access and can be
deactivated to disable output data if necessary.
FAST-PAGE-MODE operations are always initiated
with a row address strobed in by the RAS# signal,
followed by a column address strobed in by CAS#, just
like for single location accesses. However, subsequent
column locations within the row may then be accessed
at the page mode cycle time. This is accomplished by
cycling CAS# while holding RAS# LOW and entering
new column addresses with each CAS# cycle. Returning
RAS# HIGH terminates the FAST-PAGE-MODE opera-
tion.
DRAM REFRESH
The supply voltage must be maintained at the speci-
fied levels, and the refresh requirements must be met in
order to retain stored data in the DRAM. The refresh
requirements are met by refreshing all 8,192 rows (E1)
or all 4,096 rows (B6) in the DRAM array at least once
every 64ms. The recommended procedure is to execute
4,096 CBR REFRESH cycles, either uniformly spaced or
grouped in bursts, every 64ms. The MT4LC8M8E1 in-
ternally refreshes two rows for every CBR cycle, whereas
STANDBY
Returning RAS# and CAS# HIGH terminates a
memory cycle and decreases chip current to a reduced
standby level. The chip is preconditioned for the next
cycle during the RAS# HIGH time.
8 Meg x 8 FPM DRAM
D19_2.p65 – Rev. 5/00
3
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2000, Micron Technology, Inc.
MICRON [ MICRON TECHNOLOGY ]
