READ ONLY MODE
When VPP is less than VCC + 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 VPP
< VCC + 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.
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.
Address access time tACC is equal to the delay from
stable addresses to valid output data. The chip enable
access time tCE 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 tACC–tOE).
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-
rithm. This mode is functional over the entire
temperature range of the device.
Standby Mode
Programming In A PROM Programmer
The device has two standby modes. The CMOS
standby mode (CE# input held at VCC ± 0.5 V), con-
sumes less than 100 µA of current. TTL standby mode
To activate this mode, the programming equipment
must force VID (11.5 V to 13.0 V) on address A9. Two
identifier bytes may then be sequenced from the device
outputs by toggling address A0 from VIL to VIH. All other
address lines must be held at VIL, and VPP must be
less than or equal to VCC + 2.0 V while using this Auto
select mode. Byte 0 (A0 = VIL) represents the manufac-
turer code and byte 1 (A0 = VIH) 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.
(CE# is held at V ) reduces the current requirements
IH
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.
Table 2. Am28F256 Auto Select Code
Code
(HEX)
Type
A0
Manufacturer Code
Device Code
V
01
IL
V
A1
IH
Am28F256
9
AMD [ AMD ]
