Device operation

M87C257

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2.9

Electronic signature

The Electronic Signature (ES) mode allows the reading out of a binary code from an

EPROM that will identify its manufacturer and type. This mode is intended for use by

programming equipment to automatically match the device to be programmed with its

corresponding programming algorithm. The ES mode is functional in the 25°C ± 5°C

ambient temperature range that is required when programming the M87C257.

To activate the ES mode, the programming equipment must force 11.5V to 12.5V on

M87C257, these two identifier bytes are given in Table 4 and can be read-out on outputs Q7

to Q0.

2.10

Erasure operation (applies for UV EPROM)

The erasure characteristics of the M87C257 is such that erasure begins when the cells are

exposed to light with wavelengths shorter than approximately 4000 Å. It should be noted

that sunlight and some type of fluorescent lamps have wavelengths in the 3000-4000 Å

range. Research shows that constant exposure to room level fluorescent lighting could

erase a typical M87C257 in about 3 years, while it would take approximately 1 week to

cause erasure when exposed to direct sunlight. If the M87C257 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 M87C257 window to prevent unintentional erasure. The recommended

erasure procedure for the M87C257 is exposure to short wave ultraviolet light which has

wavelength 2537Å. The integrated dose (i.e. UV intensity x exposure time) for erasure

should 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.