FUJITSU Semiconductor Controller MB89950/950A - Manual (Page 307)

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APPENDIX D Programming Specifications for One-Time PROM And EPROM Microcontroller
D.2 Programming Yield and Erasure
This section describes the programming yield and the data erasure on EPROM
microcomputer.
■ Programming yield
All bits cannot be programmed at Fujitsu shipping test to a blanked OTPROM microcomputer, due to its
nature. For this reason, a programming yield of 100% cannot be assured at all times.
■ Notes on using and data erasure on EPROM microcomputer
●
Erasure
In order to clear all locations of their programmed contents, it is necessary to expose the internal EPROM
to an ultraviolet light source. A dosage of 10 W-seconds/cm
2
is required to completely erase an internal
EPROM. This dosage can be obtained by exposure to an ultraviolet lamp (wavelength of 2537 Angstroms
( )) with intensity of 12000
µW/cm 2
for 15 to 21 minutes. The internal EPROM should be about one inch
from the source and all filters should be removed from the UV light source prior to erasure.
It is important to note that the internal EPROM and similar devices, will erase with light sources having
wavelengths shorter than 4000 . Although erasure time will be much longer than with UV source at 2537
, nevertheless the exposure to fluorescent light and sunlight will eventually erase the internal EPROM,
and exposure to them should be prevented to realize maximum system reliability. If used in such an
environment, the package windows should be covered by an opaque label or substance.