ERASURE CHARACTERISTICS

The erasure characteristics of the device are such that era-

sure begins to occur when exposed to light with wave-

lengths shorter than approximately 4000 Angstroms ( ) It

should be noted that sunlight and certain types of fluores-

cent lamps have wavelengths in the 3000 – 4000

range

The recommended erasure procedure for the EPROM is ex-

posure to short wave ultraviolet light which has a wave-

length of 2537

exposure

time)

for

erasure

should

be

minimum

of

The EPROM should be placed within 1 inch of the lamp

tubes during erasure Some lamps have a filter on their

tubes which should be removed before erasure Table III

shows the minimum EPROM erasure time for various light

intensities

An erasure system should be calibrated periodically The

distance from lamp to device should be maintained at one

inch The erasure time increase as the square of the dis-

tance from the lamp (if distance is doubled the erasure time

increases by factor of 4) Lamps lose intensity as they age

When a lamp is changed the distance has changed or the

lamp has aged the system should be checked to make cer-

tain full erasure is occurring Incomplete erasure will cause

symptoms that can be misleading Programmers compo-

nents and even system designs have been erroneously

suspected when incomplete erasure was the problem

SYSTEM CONSIDERATION

The power switching characteristics of EPROMs require

has three segments that are of interest to the system de-

signer the standby current level the active current level

and the transient current peaks that are produced by volt-

age transitions on input pins The magnitude of these tran-

sient current peaks is dependent of the output capacitance

peaks can be suppressed by properly selected decoupling

capacitors It is recommended that at least a 01 mF ceramic

This should be a high frequency capacitor of low inherent

inductance In addition at least a 47 mF bulk electrolytic

eight devices The bulk capacitor should be located near

where the power supply is connected to the array The pur-

pose of the bulk capacitor is to overcome the voltage drop

caused by the inductive effects of the PC board traces

Mode Selection

The modes of operation of the NM27C512 are listed in Table I A single 5V power supply is required in the read mode All

TABLE I Mode Selection

Pins

CE PGM

Outputs

Mode

Read

50V

Output Disable

X

50V

High Z

(Note 1)

Standby

X

50V

High Z

Programming

1275V

625V

Program Verify

625V

Program Inhibit

1275V

625V

High Z

Note 1

TABLE II Manufacturer’s Identification Code

Pins

A0

A9

07

06

05

04

03

02

01

00

Hex

(10)

(24)

(19)

(18)

(17)

(16)

(15)

(13)

(12)

(11)

Data

Manufacturer Code

12V

10001111

8F

Device Code

12V

10000101

85

8