AM27X256 Advanced Micro Devices, AM27X256 Datasheet - Page 4

• Manufacturer Part Number: AM27X256
• Description: 256 Kilobit (32 K x 8-Bit) CMOS ExpressROM Device
• Manufacturer: Advanced Micro Devices

FUNCTIONAL DESCRIPTION
Read Mode
To obtain data at the device outputs, Chip Enable (CE#)
and Output Enable (OE#) must be driven low. CE# con-
trols the power to the device and is typically used to se-
lect the device. OE# enables the device to output data,
independent of device selection. Addresses must be
stable for at least t
Waveforms section for the timing diagram.
Standby Mode
The device enters the CMOS standby mode when CE#
is at V
100 µA. The device enters the TTL-standby mode
when CE# is at V
to 1.0 mA. When in either standby mode, the device
places its outputs in a high-impedance state, indepen-
dent of the OE# input.
Output OR-Tieing
To accommodate multiple memory connections, a
two-line control function provides:
MODE SELECT TABLE
Note:
X = Either V
4
Mode
Read
Output Disable
Standby (TTL)
Standby (CMOS)
Low memory power dissipation, and
Assurance that output bus contention will not occur.
CC
IH
0.3 V. Maximum V
or V
IL
IH
.
. Maximum V
ACC
–t
OE
. Refer to the Switching
CC
CC
current is reduced to
current is reduced
V
CC
Am27X256
CE#
V
V
X
IH
IL
0.3 V
CE# should be decoded and used as the primary de-
vice-selecting function, while OE# be made a common
connection to all devices in the array and connected to
the READ line from the system control bus. This as-
sures that all deselected memory devices are in their
low-power standby mode and that the output pins are
only active when data is desired from a particular mem-
ory device.
System Applications
During the switch between active and standby condi-
tions, transient current peaks are produced on the ris-
ing 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
V
to overcome the voltage drop caused by the inductive
effects of the printed circuit board traces on Express-
ROM device arrays, a 4.7 µF bulk electrolytic capacitor
should be used between V
devices. The location of the capacitor should be close
to where the power supply is connected to the array.
CC
and V
OE#
V
V
SS
X
X
IH
IL
to minimize transient effects. In addition,
V
X
X
X
X
CC
PP
and V
SS
for each eight
Outputs
High Z
High Z
High Z
D
OUT