AT28C010 Com/Ind
3
Device Operation
READ: The AT28C010 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 the high
impedance state when either CE
or OE is high. This dual-
line control gives designers flexibility in preventing bus con-
tention in their system.
BYTE WRITE: A low pulse on the WE
or CE input with CE
or WE low (respectively) and OE high initiates a write cycle.
The address is latched on the falling edge of CE
or WE,
whichever occurs last. The data is latched by the first rising
edge of CE
or WE. 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.
PAGE WRITE: The page write operation of the AT28C010
allows 1 to 128 bytes of data to be written into the device
during a single internal programming period. A page write
operation is initiated in the same manner as a byte write;
the first byte written can then be followed by 1 to 127 addi-
tional bytes. Each successive byte must be written within
150
µ
s (t
BLC
) of the previous byte. If the t
BLC
limit is
exceeded the AT28C010 will cease accepting data and
commence the internal programming operation. All bytes
during a page write operation must reside on the same
page as defined by the state of the A7 - A16 inputs. For
each WE
high to low transition during the page write opera-
tion, A7 - A16 must be the same.
The A0 to A6 inputs are used to specify which bytes within
the page are to be written. The bytes may be loaded in any
order and may be altered within the same load period. Only
bytes which are specified for writing will be written; unnec-
essary cycling of other bytes within the page does not
occur.
DATA
POLLING: The AT28C010 features DATA Polling to
indicate the end of a write cycle. During a byte or page
write cycle an attempted read of the last byte written will
result in the complement of the written data to be presented
on I/O
7
. Once the write cycle has been completed, true
data is valid on all outputs, and the next write cycle may
begin. DATA
Polling may begin at anytime during the write
cycle.
TOGGLE BIT: In addition to DATA
Polling the AT28C010
provides another method for determining the end of a write
cycle. During the write operation, successive attempts to
read data from the device will result in I/O
6
toggling
between one and zero. Once the write has completed, I/O
6
will stop toggling and valid data will be read. Reading the
toggle bit may begin at any time during the write cycle.
DATA PROTECTION: If precautions are not taken, inad-
vertent writes may occur during transitions of the host sys-
tem power supply. Atmel has incorporated both hardware
and software features that will protect the memory against
inadvertent writes.
HARDWARE PROTECTION: Hardware features protect
against inadvertent writes to the AT28C010 in the following
ways: (a) V
CC
sense—if V
CC
is below 3.8V (typical) the
write function is inhibited; (b) V
CC
power-on delay—once
V
CC
has reached 3.8V the device will automatically time out
5 ms (typical) before allowing a write; (c) write inhibit—
holding any one of OE
low, CE high or WE high inhibits
write cycles; and (d) noise filter—pulses of less than 15 ns
(typical) on the WE
or CE inputs will not initiate a write
cycle.
SOFTWARE DATA PROTECTION: A software controlled
data protection feature has been implemented on the
AT28C010. When enabled, the software data protection
(SDP), will prevent inadvertent writes. The SDP feature
may be enabled or disabled by the user; the AT28C010 is
shipped from Atmel with SDP disabled.
SDP is enabled by the host system issuing a series of three
write commands; three specific bytes of data are written to
three specific addresses (refer to Software Data Protection
Algorithm). After writing the 3-byte command sequence
and after t
WC
the entire AT28C010 will be protected against
inadvertent write operations. It should be noted, that once
protected the host may still perform a byte or page write to
the AT28C010. This is done by preceding the data to be
written by the same 3-byte command sequence used to
enable SDP.
Once set, SDP will remain active unless the disable com-
mand sequence is issued. Power transitions do not disable
SDP and SDP will protect the AT28C010 during power-up
and power-down conditions. All command sequences must
conform to the page write timing specifications. The data in
the enable and disable command sequences is not written
to the device and the memory addresses used in the
sequence may be written with data in either a byte or page
write operation.
After setting SDP, any attempt to write to the device without
the 3-byte command sequence will start the internal write
timers. No data will be written to the device; however, for
the duration of t
WC
, read operations will effectively be poll-
ing operations.
DEVICE IDENTIFICATION: An extra 128 bytes of
EEPROM memory are available to the user for device iden-
tification. By raising A9 to 12V ± 0.5V and using address
locations 1FF80H to 1FFFFH the bytes may be written to or
read from in the same manner as the regular memory
array.
OPTIONAL CHIP ERASE MODE: The entire device can
be erased using a 6-byte software code. Please see Soft-
ware Chip Erase application note for details.
