4 MEG x 16, 2 MEG x 16
ASYNC/PAGE/BURST CellularRAM MEMORY
ADVANCE
09005aef80be2036/09005aef80be1fbd Micron Technology, Inc., reserves the right to change products or specifications without notice.
Burst CellularRAM.fm - Rev. A 7/03 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 and there ar e no transactions in progress.
The device will enter standby operation upon com-
pletion of a READ or WRITE operation, or when the
address and control inputs remain static for an
extended period of time. This “active” standby mode
will continue until a change occurs to the address or
control inputs.
Temperature Compensated Refresh
Temperature compensated refresh ( TCR) is used to
adjust the refr esh r ate dependi ng on the de vice oper at-
ing temperature. DRAM technology requires increas-
ingly frequent refresh operations to maintain data
integrity as temperatures increase. More frequent
refresh is required due to increased leakage of the
DRAM capacitive storage elements as temperatures
rise. A decreased refresh rate at lower temperatures
will facilitate a savings in standby curr ent.
TCR allows for adequate refresh at four different
temperature thresholds (+15°C, +45°C, +70°C, and
+85°C). The setting selected must be for a temperature
higher than the case temperature of the CellularRAM
device. If the case temperature is +50°C, the system can
minimize self refr esh current consumption by selecting
the +70°C setting. The +15°C and +45°C settings would
result in inadequate refreshing and cause data corrup-
tion.
Partial Array Refresh
Partial array refresh (PAR) restricts refresh operation
to a portion of the total memory array. This feature
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,
three-quarters array, one-half array, one-quar ter array,
or none of the array. The mapping of these partitions
can start at either the beginning or the end of the
address map (see Tables 9 and 10 on page 21). READ
and WRITE operations to address ranges receiving
refresh will not be affected. Data stored in addresses
not receiving refresh will become corrupted.
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, the CellularRAM device will require 150µs
to perform an initialization procedure before normal
operations can resume. During this 150µs period, the
current consumption will be higher than the specified
standby levels, but considerably lower than the active
current specification.
Configuration Registers
Two WRITE-only, user-accessible configuration reg-
isters have been included to define device operation.
The bus configuration register (BCR) defines how the
CellularRAM interacts with the system memory bus and
is nearly identical to its counterpart on burst mode
Flash devices. The refresh configuration 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.
Bus Configuration Register
The BCR defines how the CellularRAM device inter-
acts with the system memory bus. Page mode opera-
tion is enabled by a bit contained in the RCR. The BCR
is loaded using either a synchronous or an asynchro-
nous WRITE operation when A[19] is HIGH and the
configuration register enable (CRE) input is also HIGH
(see Figures 12 and 13 on page 15). When CRE is LOW,
a READ or WRITE operation will access the memory
array. The values placed on address pins A[21:0] are
latched into the BCR on the rising edge of ADV#, CE#,
or WE#, whichever occurs first. LB# and UB# ar e “ Don’t
Care.” Table 5 on page 16 describes the control bits in
the BCR. At power-up, the BCR is set to 9F4Fh.