M27W256

6/15

Figure 5. Read Mode AC Waveforms

AI00758B

tAXQX

tEHQZ

A0-A14

E

G

Q0-Q7

tAVQV

tGHQZ

tGLQV

tELQV

VALID

Hi-Z

VALID

Two Line Output Control

Because EPROMs are usually used in larger

memory arrays, this product features a 2 line con-

trol function which accommodates the use of mul-

tiple memory connection. The two line control

function allows:

a. the lowest possible memory power dissipation,

b. complete assurance that output bus contention

will not occur.

For the most efficient use of these two control

lines, E should be decoded and used as the prima-

ry device selecting function, while G should be

made a common connection to all devices in the

array and connected to the READ line from the

system control bus. This ensures that all deselect-

ed memory devices are in their low power standby

mode and hat the output pins are only active when

data is desired from a particular memory device.

System Considerations

The power switching characteristics of Advance

CMOS EPROMs require careful decoupling of the

ments that are of interest to the system designer:

the standby current level, the active current level,

and transient current peaks that are produced by

the falling and rising edges of E. The magnitude of

this transient current peaks is dependent on the

capacitive and inductive loading of the device at

the output. The associated transient voltage peaks

can be suppressed by complying with the two line

output control and by properly selected decoupling

capacitors. It is recommended that a 0.1

µF ceram-

tor of low inherent inductance and should be

placed as close to the device as possible. In addi-

tion, a 4.7

µF bulk electrolytic capacitor should be

es. The bulk capacitor should be located near the

power supply connection point. The purpose of the

bulk capacitor is to overcome the voltage drop

caused by the inductive effects of PCB traces.