M27C2001(1995) データシートの表示（PDF） - STMicroelectronics

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M27C2001
(Rev.:1995)

2 Megabit (256K x 8) UV EPROM and OTP ROM

STMicroelectronics 

M27C2001

Figure 7. Programming Flowchart

VCC = 6.25V, VPP = 12.5V

n =0

NO

++n

= 25

YES

P = 100µs Pulse

NO

VERIFY

YES

++ Addr

FAIL

Last NO

Addr

YES

CHECK ALL BYTES

1st: VCC = 6V

2nd: VCC = 4.2V

AI00715B

Program Verify

A verify (read) should be performed on the pro-

grammed bits to determine that they were correctly

programmed. The verify is accomplished with E

and G at VIL, P at VIH, VPP at 12.75V and VCC at

6.25V.

Electronic Signature

The Electronic Signature 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.

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

temperature range that is required when program-

ming the M27C2001. To activate this mode, the

programming equipmentmust force 11.5Vto 12.5V

on address line A9 of the M27C2001 with

VPP=VCC=5V. Two identifier bytes may then be

sequenced from the device outputs by toggling

address line A0 from VIL to VIH. All other address

lines must be held at VIL during Electronic Signa-

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

facturer code and byte 1 (A0=VIH) the device

identifier code. For the SGS-THOMSON

M27C2001, these two identifier bytes are given in

Table 4 and can be read-out on outputs Q0 to Q7.

PRESTO II Programming Algorithm

PRESTO II Programming Algorithm allows the

whole array to be programmed with a guaranteed

margin, in a typical time of 26.5 seconds. Program-

ming with PRESTO II consists of applying a se-

quence of 100µs program pulses to each byte until

a correct verify occurs. During programming and

verify operation, a MARGIN MODE circuit is auto-

matically activated in order to guarantee that each

cell is programmed with enough margin. No over-

program pulse is applied since the verify in MAR-

GIN MODE provides the necessary margin to each

programmed cell.

Program Inhibit

Programming of multiple M27C2001s in parallel

with different data is also easily accomplished.

Except for E, all like inputs including G of the

parallel M27C2001 may be common. A TTL low

level pulse applied to a M27C2001’s E input, with

P low and VPP at 12.75V, will program that

M27C2001. A high level E input inhibits the other

M27C2001s from being programmed.

ERASURE OPERATION (applies to UV EPROM)

The erasure characteristics of the M27C2001 are

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 3000-4000Å range. Data shows that

constant exposure to room level fluorescent light-

ing could erase a typical M27C2001 in about 3

years, while it would take approximately 1 week to

cause erasure when exposed to direct sunlight. If

the M27C2001 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

M27C2001 window to prevent unintentional era-

sure. The recommended erasure procedure for the

M27C2001 is exposure to short wave ultraviolet

light which has 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 M27C2001

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.

8/14

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