READ ONLY MODE
When V
PP
is less than V
CC
+ 2 V, the command register
is inactive. The device can either read array or autose-
lect data, or be standby mode.
Output Disable
Output from the device is disabled when OE# is at a
logic high level. When disabled, output pins are in a
high impedance state.
Read
The device functions as a read only memory when V
PP
< V
CC
+ 2 V. The device has two control functions. Both
must be satisfied in order to output data. CE# controls
power to the device. This pin should be used for spe-
cific device selection. OE# controls the device outputs
and should be used to gate data to the output pins if a
device is selected.
Address access time t
ACC
is equal to the delay from
stable addresses to valid output data. The chip enable
access time t
CE
is the delay from stable addresses and
stable CE# to valid data at the output pins. The output
enable access time is the delay from the falling edge of
OE# to valid data at the output pins (assuming the ad-
dresses have been stable at least t
ACC
–t
OE
).
Auto Select
Flash memories can be programmed in-system or in a
standard PROM programmer. The device may be sol-
dered to the circuit board upon receipt of shipment and
programmed in-system. Alternatively, the device may
initially be programmed in a PROM programmer prior
to soldering the device to the board.
The Auto select mode allows the reading out of a binary
code from the device that will identify its manufacturer
and type. This mode is intended for the purpose
of automatically matching the device to be pro-
grammed with its corresponding programming algo-
r ith m. Th is mo de is f unc tio nal ove r t he en tir e
temperature range of the device.
Standby Mode
The device has two standby modes. The CMOS
standby mode (CE# input held at V
CC
±
0.5 V), con-
sumes less than 100 µA of current. TTL standby mode
(CE# is held at V
IH
) reduces the current requirements
to less than 1mA. When in the standby mode the out-
puts are in a high impedance state, independent of the
OE# input.
If the device is deselected during erasure, program-
ming, or program/erase verification, the device will
draw active current until the operation is terminated.
Programming In A PROM Programmer
To activate this mode, the programming equipment
must force V
ID
(11.5 V to 13.0 V) on address A9. Two
identifier bytes may then be sequenced from the device
outputs by toggling address A
0
from V
IL
to V
IH
. All other
address lines must be held at V
IL
, and V
PP
must be
less than or equal to V
CC
+ 2.0 V while using this Auto
select mode. Byte 0 (A0 = V
IL
) represents the manufac-
turer code and byte 1 (A0 = V
IH
) the device identifier
code. For the device these two bytes are given in Table
2 below. All identifiers for manufacturer and device
codes will exhibit odd parity with the MSB (DQ7) de-
fined as the parity bit.
Table 2.
Type
Manufacturer Code
Device Code
Am28F256 Auto Select Code
A0
V
IL
V
IH
Code
(HEX)
01
A1
Am28F256
9
AMD [ ADVANCED MICRO DEVICES ]
