E
28F010
9
Table 2. 28F010 Bus Operations
Mode
V
PP(1)
A
0
A
9
CE#
OE#
WE#
DQ
0
–DQ
7
Read
V
PPL
A
0
A
9
V
IL
V
IL
V
IH
Data Out
Output Disable
V
PPL
X
X
V
IL
V
IH
V
IH
Tri-State
READ-ONLY
Standby
V
PPL
X
X
V
IH
X
X
Tri-State
Intelligent Identifier (Mfr)
(2)
V
PPL
V
IL
V
ID(3)
V
IL
V
IL
V
IH
Data = 89H
Intelligent Identifier (Device)
(2)
V
PPL
V
IH
V
ID(3)
V
IL
V
IL
V
IH
Data = B4H
Read
V
PPH
A
0
A
9
V
IL
V
IL
V
IH
Data Out
(4)
READ/WRITE Output Disable
V
PPH
X
X
V
IL
V
IH
V
IH
Tri-State
Standby
(5)
V
PPH
X
X
V
IH
X
X
Tri-State
Write
V
PPH
A
0
A
9
V
IL
V
IH
V
IL
Data In
(6)
NOTES:
1.
2.
Refer to DC Characteristics When V
PP
= V
PPL
memory contents can be read but not written or erased.
Manufacturer and device codes may also be accessed via a command register write sequence. Refer to Table 3. All other
addresses low.
V
ID
is the intelligent identifier high voltage. Refer to DC Characteristics
Read operations with V
PP
= V
PPH
may access array data or the intelligent identifier codes.
With V
PP
at high voltage, the standby current equals I
CC
+ I
PP
(standby).
Refer to Table 3 for valid data-in during a write operation.
X can be V
IL
or V
IH
.
3.
4.
5.
6.
7.
2.2
Write Protection
The command register is only active when V
PP
is at
high voltage. Depending upon the application, the
system designer may choose to make the V
PP
power supply switchable
—available only when
memory updates are desired. When V
PP
= V
PPL
, the
contents of the register default to the Read
command, making the 28F010 a read-only memory.
In this mode, the memory contents cannot be
altered.
Or, the system designer may choose to “hardwire”
V
PP
, making the high voltage supply constantly
available. In this case, all command register
functions are inhibited whenever V
CC
is below the
write lockout voltage V
LKO
. (See Section 3.4,
Power-Up/Down
Protection
.)
designed to accommodate either design practice,
and to encourage optimization of the processor
memory interface.
The
28F010
is
The two-step program/erase write sequence to the
command register provides additional software
write protections.
2.2.1
BUS OPERATIONS
2.2.1.1
Read
The 28F010 has two control functions, both of
which must be logically active, to obtain data at the
outputs. Chip Enable (CE#) is the power control
and should be used for device selection. Output
Enable (OE#) is the output control and should be
used to gate data from the output pins, independent
of device selection. Refer to the AC read timing
waveforms.
When V
PP
is high (V
PPH
), the read operation can be
used to access array data, to output the intelligent
identifier
codes,
and
program/erase verification. When V
PP
is low (V
PPL
),
the read operation can
only
access the array data.
to
access
data
for
2.2.1.2
Output Disable
With OE# at a logic-high level (V
IH
), output from the
device is disabled. Output pins are placed in a high-
impedance state.