2 MEG x 16
ASYNC/PAGE/BURST CellularRAM MEMORY
ADVANCE
09005aef80ec6f63
Micron Technology, Inc., reserves the right to change products or specifications without notice.
Burst CellularRAM_32.fm - Rev. A 2/18/04 EN
12
2004 Micron Technology, Inc. All Rights Reserved.
Mixed-Mode Operation
The device can support a combination of synchro-
nous READ and asynchronous WRITE operations
when the BCR is configured for synchronous opera-
tion. The asynchronous WRITE operation requires that
the clock (CLK) remain static (HIGH or LOW) during
the entire sequence. The ADV# signal can be used to
latch the target address, or it can remain LOW during
the entire WRITE operation. CE# must return HIGH
when transitioning between mixed-mode operations.
Note that the tCKA period is the same as a READ or
WRITE cycle. This time is required to ensure adequate
refresh. Mixed-mode operation facilitates a seamless
interface to legacy burst mode Flash memory control-
WRITE Followed by Burst READ” timing diagram.
WAIT Operation
The WAIT output on a CellularRAM device is typi-
cally connected to a shared, system-level WAIT signal
(see
Figure 9 below). The shared WAIT signal is used by
the processor to coordinate transactions with multiple
memories on the synchronous bus.
Figure 9: Wired or WAIT Configuration
Once a READ or WRITE operation has been initi-
ated, WAIT goes active to indicate that the Cellular-
RAM device requires additional time before data can
be transferred. For READ operations, WAIT will remain
active until valid data is output from the device. For
WRITE operations, WAIT will indicate to the memory
controller when data will be accepted into the Cellu-
larRAM device. When WAIT transitions to an inactive
state, the data burst will progress on successive clock
edges.
CE# must remain asserted during WAIT cycles
(WAIT asserted and WAIT configuration BCR[8] = 1).
Bringing CE# HIGH during WAIT cycles may cause
data corruption. (Note that for BCR[8] = 0, the actual
WAIT cycles end one cycle after WAIT deasserts, and
for row boundary crossings, start one cycle after the
WAIT signal asserts.)
The WAIT output also performs an arbitration role
when a READ or WRITE operation is launched while
an on-chip refresh is in progress. If a collision occurs,
the WAIT pin is asserted for additional clock cycles
until the refresh has completed (see Figures
10 and
11on
page 13). When the refresh operation has com-
pleted, the READ or WRITE operation will continue
normally.
WAIT is also asserted when a continuous READ or
WRITE burst crosses a row boundary. The WAIT asser-
tion allows time for the new row to be accessed, and
permits any pending refresh operations to be per-
formed.
LB#/UB# Operation
The LB# enable and UB# enable signals support
byte-wide data transfers. During READ operations, the
enabled byte(s) are driven onto the DQs. The DQs
associated with a disabled byte are put into a High-Z
state during a READ operation. During WRITE opera-
tions, any disabled bytes will not be transferred to the
RAM array and the internal value will remain
unchanged. During an asynchronous WRITE cycle, the
data to be written is latched on the rising edge of CE#,
WE#, LB#, or UB#, whichever occurs first.
When both the LB# and UB# are disabled (HIGH)
during an operation, the device will disable the data
bus from receiving or transmitting data. Although the
device will seem to be deselected, it remains in an
active mode as long as CE# remains LOW.
CellularRAM
External
Pull-Up/
Pull-Down
Resistor
Processor
READY
Other
Device
WAIT
Other
Device
WAIT