AMD27C256 Datasheet, PDF (7/12 Pages) Advanced Micro Devices – 256 Kilobit (32,768 x 8-Bit) CMOS EPROM

AMD
Output OR-Tieing
To accommodate multiple memory connections, a two-
line control function is provided to allow for:
s Low memory power dissipation
s Assurance that output bus contention will not occur
It is recommended that CE be decoded and used as the
primary device-selecting function, while OE be made a
common connection to all devices in the array and con-
nected to the READ line from the system control bus.
This assures that all deselected memory devices are in
low-power standby mode and that the output pins are
only active when data is desired from a particular
memory device.
System Applications
During the switch between active and standby condi-
tions, transient current peaks are produced on the rising
and falling edges of Chip Enable. The magnitude of
these transient current peaks is dependent on the out-
put capacitance loading of the device. At a minimum, a
0.1-µF ceramic capacitor (high frequency, low inherent
inductance) should be used on each device between
VCC and VSS to minimize transient effects. In addition, to
overcome the voltage drop caused by the inductive ef-
fects of the printed circuit board traces on EPROM ar-
rays, a 4.7-µF bulk electrolytic capacitor should be used
between VCC and VSS for each eight devices. The loca-
tion of the capacitor should be close to where the power
supply is connected to the array.
MODE SELECT TABLE
Mode
Pins
CE
OE
A0
A9
Read
VIL
VIL
X
X
Output Disable
X
VIH
X
X
Standby (TTL)
VIH
X
X
X
Standby (CMOS)
VCC + 0.3 V
X
X
X
Program
VIL
VIH
X
X
Program Verify
VIH
VIL
X
X
Program Inhibit
VIH
VIH
X
X
Auto Select
(Note 3)
Manufacturer
Code
Device Code
VIL
VIL
VIL
VH
VIL
VIL
VIH
VH
Notes:
1. VH = 12.0 V + 0.5 V
2. X = Either VIH or VIL
3. A1–A8 = A10–A14 = VIL
4. See DC Programming Characteristics for VPP voltage during programming.
VPP
Outputs
X
DOUT
X
High-Z
X
High-Z
X
High-Z
VPP
DIN
VPP
DOUT
VPP
High-Z
X
01H
X
10H
2-38
Am27C256