
2 MEG x 16
ASYNC/PAGE/BURST CellularRAM MEMORY
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Burst CellularRAM_32__2.fm - Rev. B 9/04 EN 14 ©2003 Micron Technology, Inc. All rights reserved.
Low-Power Operation
Standby Mode Operation
During standby, the device current consumption is
reduced to the level necessary to perform the DRAM
refresh operation. Standby operation occurs when CE#
is HIGH.
The device will enter a reduced power state upon
completion of a READ or WRITE operation, or when
the address and control inputs remain static for an
extended period of time. This mode will continue until
a change occurs to the address or control inputs.
Temperature Compensated Refresh
Temperature compensated refresh (TCR) allows for
adequate refresh at different temperatures. This
CellularRAM device includes an on-chip temperature
sensor. When the sensor is enabled, it continually
adjusts the refresh rate according to the operating
temperature. The on-chip sensor is enabled by default.
Three fixed refresh rates are also available, corre-
sponding to temperature thresholds of +15°C, +45°C,
and +85°C. The setting selected must be for a tempera-
ture higher than the case temperature of the Cellular-
RAM device. If the case temperature is +35°C, the
system can minimize self-refresh current consump-
tion by selecting the +45°C setting. The +15°C setting
would result in inadequate refreshing and cause data
corruption.
Partial Array Refresh
Partial array refresh (PAR) restricts refresh opera-
tion to a portion of the total memory array. This fea-
ture enables the device to reduce standby current by
refreshing only that part of the memory array required
by the host system. The refresh options are full array,
one-half array, one-quarter array, one-eighth, or none
of the array. The mapping of these partitions can start
at either the beginning or the end of the address map
(see Table 6 on page 23). READ and WRITE operations
to address ranges receiving refresh will not be affected.
Data stored in addresses not receiving refresh will
become corrupted. When re-enabling additional por-
tions of the array, the new portions are available
immediately upon writing to the RCR.
Deep Power-Down Operation
Deep power-down (DPD) operation disables all
refresh-related activity. This mode is used if the system
does not require the storage provided by the Cellular-
RAM device. Any stored data will become corrupted
when DPD is enabled. When refresh activity has been
re-enabled by rewriting the RCR, the CellularRAM
device will require 150µs to perform an initialization
procedure before normal operations can resume. Dur-
ing this 150µs period, the current consumption will be
higher than the specified standby levels, but consider-
ably lower than the active current specification.
DPD cannot be enabled or disabled by writing to
the RCR using the software access sequence; the RCR
should be accessed using CRE instead.
Configuration Registers
Two user-accessible configuration registers define
the device operation. The bus configuration register
(BCR) defines how the CellularRAM interacts with the
system memory bus and is nearly identical to its coun-
terpart on burst mode Flash devices. The refresh config-
uration register (RCR) is used to control how refresh is
performed on the DRAM array. These registers are
automatically loaded with default settings during
power-up, and can be updated any time the devices
are operating in a standby state.
Access Using CRE
The configuration registers are loaded using either a
synchronous or an asynchronous WRITE operation
when the configuration register enable (CRE) input is
HIGH (see Figures 13 and 14 on page 16). When CRE is
LOW, a READ or WRITE operation will access the
memory array. The register values are placed on
address pins A[20:0]. In an asynchronous WRITE, the
values are latched into the configuration register on
the rising edge of ADV#, CE#, or WE#, whichever
occurs first; LB# and UB# are “Don’t Care.” Access
using CRE is WRITE only. The BCR is accessed when
A[19] is HIGH; the RCR is accessed when A[19] is LOW.