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Am27X64

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

Waveforms section for the timing diagram.

Standby Mode

The device enters the CMOS standby mode when CE#

100 µA. The device enters the TTL-standby mode

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:

s Low memory power dissipation, and

s Assurance that output bus contention will not occur.

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

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

devices. The location of the capacitor should be close

to where the power supply is connected to the array.

MODE SELECT TABLE

Note:

Mode

CE#

OE#

PGM#

Outputs

Read

XX

Output Disable

X

X

X

High Z

Standby (TTL)

X

X

X

High Z

Standby (CMOS)

X

X

X

High Z