M27W400 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
M27W400 Datasheet PDF : 15 Pages
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M27W400
Figure 9. Programming Flowchart
VCC = 6.25V, VPP = 12.5V
n=0
NO
++n
= 25
YES
E = 50µs Pulse
NO
VERIFY
YES
++ Addr
FAIL
Last NO
Addr
YES
CHECK ALL WORDS
BYTEVPP =VIH
1st: VCC = 5V
2nd: VCC = 2.7V
AI03600
PRESTO III Programming Algorithm
The PRESTO III Programming Algorithm allows
the whole array to be programed with a guaran-
teed margin in a typical time of 26 seconds. Pro-
gramming with PRESTO III consists of applying a
sequence of 50µs program pulses to each word
until a correct verify occurs (see Figure 9). During
programing and verify operation a MARGIN
MODE circuit is automatically activated to guaran-
tee that each cell is programed with enough mar-
gin. No overpromise pulse is applied since the
verify in MARGIN MODE provides the necessary
margin to each programmed cell.
Program Inhibit
Programming of multiple M27W400s in parallel
with different data is also easily accomplished. Ex-
cept for E, all like inputs including G of the parallel
M27W400 may be common. A TTL low level pulse
applied to a M27W400's E input and VPP at 12.5V,
will program that M27W400. A high level E input
inhibits the other M27W400s from being pro-
grammed.
Program Verify
A verify (read) should be performed on the pro-
grammed bits to determine that they were correct-
ly programmed. The verify is accomplished with E
at VIH and G at VIL, VPP at 12.5V and VCC at
6.25V.
On-Board Programming
The M27W400 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 corresponding programming algorithm.
The ES mode is functional in the 25°C ± 5°C am-
bient temperature range that is required when pro-
gramming the M27W400. To activate the ES
mode, the programming equipment must force
11.5V to 12.5V on address line A9 of the
M27W400, with VPP = VCC = 5V. Two identifier
bytes may then be sequenced from the device out-
puts by toggling address 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 manufacturer
code and byte 1 (A0 = VIH) the device identifier
code. For the STMicroelectronics M27W400,
these two identifier bytes are given in Table 4 and
can be read-out on outputs Q7 to Q0.
ERASURE OPERATION (applies to UV EPROM)
The erasure characteristics of the M27W400 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
wavelengths in the 3000-4000 Å range. Research
shows that constant exposure to room level fluo-
rescent lighting could erase a typical M27W400 in
about 3 years, while it would take approximately 1
week to cause erasure when exposed to direct
sunlight. If the M27W400 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 M27W400 window to prevent unintentional
erasure. The recommended erasure procedure for
M27W400 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 30 W-sec/cm2.
The erasure time with this dosage is approximate-
ly 30 to 40 minutes using an ultraviolet lamp with
12000 µW/cm2 power rating. The M27W400
should be placed within 2.5cm (1 inch) of the lamp
tubes during the erasure. Some lamps have a filter
on their tubes which should be removed before
erasure.
10/15
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