AT28BV16
3
Device Operation
READ:
The AT28BV16 is accessed like a Static RAM.
When CE
and OE are low and WE is high, the data stored
at the memory location determined by the address pins is
asserted on the outputs. The outputs are put in a high
impedance state whenever CE
or OE is high. This dual line
control gives designers increased flexibility in preventing
bus contention.
BYTE WRITE:
Writing data into the AT28BV16 is similar
to writing into a Static RAM. A low pulse on the WE
or CE
input with OE high and CE or WE low (respectively) ini-
tiates a byte write. The address location is latched on the
last falling edge of WE
(or CE); the new data is latched on
the first rising edge. Internally, the device performs a self-
clear before write. Once a byte write has been started, it
will automatically time itself to completion. Once a pro-
gramming operation has been initiated and for the duration
of t
WC
, a read operation will effectively be a polling opera-
tion.
DATA
POLLING:
The AT28BV16 provides DATA
POLL-
ING to signal the completion of a write cycle. During a write
cycle, an attempted read of the data being written results in
the complement of that data for I/O
7
(the other outputs are
indeterminate). When the write cycle is finished, true data
appears on all outputs.
READY/BUSY
(TSOP only)
:READY/BUSY
is an open
drain output; it is pulled low during the internal write cycle
and released at the completion of the write cycle.
WRITE PROTECTION:
Inadvertent writes to the device
are protected against in the following ways: (a) V
CC
sense—if V
CC
is below 2.0V (typical) the write function is
inhibited; (b) V
CC
power on delay—once V
CC
has reached
2.0V the device will automatically time out 5 ms (typical)
before allowing a byte write; and (c) Write Inhibit—holding
any one of OE
low, CE high or WE high inhibits byte write
cycles.
DEVICE IDENTIFICATION:
An extra 32-bytes of
EEPROM memory are available to the user for device iden-
tification. By raising A9 to 12 ± 0.5V and using address
locations 7E0H to 7FFH the additional bytes may be written
to or read from in the same manner as the regular memory
array.