M27C256B_98 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

M27C256B_98

256 Kbit (32Kb x 8) UV EPROM and OTP EPROM

STMicroelectronics 

M27C256B

On-Board Programming

The M27C256B can be directly programmed in the

application circuit. See the relevant Application

Note AN620.

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 correspondingprogramming algorithm. The

ES mode is functional in the 25°C ± 5°C ambient

temperature range that is required when program-

ming the M27C256B. To activate the ES mode, the

programming equipmentmust force 11.5Vto 12.5V

on address line A9 of the M27C256B, with VCC =

VPP = 5V. Two identifier bytes may then be se-

quenced from the device outputs by toggling ad-

dress line A0 from VIL to VIH. All other address lines

must be held at VIL during Electronic Signature

mode. Byte 0 (A0=VIL) represents the manufac-

turer code and byte 1 (A0=VIH) the device identifier

code. For the STMicroelectronics M27C256B,

these two identifier bytes are given in Table 4 and

can be read-out on outputs Q0 to Q7.

ERASURE OPERATION (applies for UV EPROM)

The erasure characteristics of the M27C256B is

such that erasure begins when the cells are ex-

posed to light with wavelengths shorter than ap-

proximately 4000 Å. It shouldbe notedthat sunlight

and some type of fluorescent lamps have wave-

lengthsin the 3000-4000Å range. Research shows

that constant exposure to room level fluorescent

lighting could erase a typical M27C256B in about

3 years, while it would take approximately 1 week

to cause erasure when exposed to direct sunlight.

If the M27C256B 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

M27C256B window to prevent unintentional era-

sure. The recommended erasure procedurefor the

M27C256B 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 a minimum of 15 W-sec/cm2. The era-

sure time with this dosage is approximately 15 to

20 minutes using an ultraviolet lamp with 12000

µW/cm2 power rating. The M27C256B 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 era-

sure.

9/15

Share Link: