27C64-150 datasheet(8/12 Pages) STMICROELECTRONICS

8 / 12 page

tAVPL

VALID

AI00779

A0-A12

Q0-Q7

VPP

VCC

DATA IN

DATA OUT

tQVPL

tVPHPL

tVCHPL

tPHQX

tPLPH

tGLQV

tQXGL

tELPL

tGHQZ

tGHAX

PROGRAM

VERIFY

Figure 6. Programming and Verify Modes AC Waveforms

AI01167

n = 1

Last

Addr

VERIFY

P = 1ms Pulse

++n

> 25

++ Addr

VCC = 6V, VPP = 12.5V

FAIL

CHECK ALL BYTES

1st: VCC = 6V

2nd: VCC = 4.2V

YES

P = 3ms Pulse by n

Figure 7. Programming Flowchart

ERASURE OPERATION (applies to UV EPROM)

The erasure characteristics of the M27C64A is

such that erasure begins when the cells are ex-

posed to light with wavelengths shorter than ap-

proximately 4000 Å. It should be noted that sunlight

and some type of fluorescent lamps have wave-

lengths in the 3000-4000 Å range.

Research

shows that constant exposure to room level fluo-

rescent lighting could erase a typical M27C64A in

about 3 years, while it would take approximately 1

week to cause erasure when exposed to direct

sunlight. If the M27C64A is to be exposed to these

types of lighting conditions for extended periods of

time, it is suggested that opaque labels be put over

the M27C64A window to prevent unintentional era-

sure. The recommended erasure procedure for

the M27C64A is exposure to short wave ultraviolet

light which has a wavelength of 2537 Å. The inte-

grated dose (i.e. UV intensity x exposure time) for

erasure should be a minimum of 15 W-sec/cm2.

The erasure time with this dosage is approximately

15 to 20 minutes using an ultraviolet lamp with

12000

µW/cm2 power rating. The M27C64Ashould

be placed within 2.5 cm (1 inch) of the lamp tubes

during the erasure. Some lamps have a filter on

their tubes which should be removed before erasure.

8/12

M27C64A

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