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M27C322
PRES TO II I Programm i ng Algorithm
The PRESTO III Programming Algorithm allows
the whole array to be programed with a guaran-
teed margin in a typical time of 100 seconds. Pro-
gramming with PRESTO I II con sists of applying a
sequence of 50µs program pulses to each word
until a correct verify occurs (see Figure 8). During
programing and verify operation a MARGIN
MODE circuit must be activated to guarantee that
each cell is programed with enough margin. No
overprogram pulse is applied since the verify in
MARGIN MODE provides the nec essary margin to
each programmed cell.
Program Inhibit
Programming of multiple M27C322s in parallel
with different data is also easily accomplished. Ex-
cept for E, all like inputs incl uding GVPP of the par-
allel M27C322 may be co mmon. A TTL low level
pulse applie d to a M27C322's E i nput and VPP at
12V, will program that M27C322. A high le vel E in-
put inhibits the other M27C322s from being pro-
grammed.
Program Verify
A verify (read) should be performed on the pro-
grammed bits to det ermine that they were correct-
ly programmed. The verify is accomplished with
Figure 8. Programming Flowchart
AI02206
n = 0
Last
Addr
VERIFY
E = 50µs Pulse
++n
= 25 ++ Addr
VCC = 6.25V, VPP = 12V
FAIL
CHECK ALL WORDS
1st: VCC = 6V
2nd: VCC = 4.2V
YES
NO
YES
NO
YES
NO
SET MARGIN MODE
RESET MARGIN MODE
GVPP at VIL. Data should be verified wit h tELQV af -
ter the falling edge of E .
On-Boa rd Progra mming
The M27C 322 can be directly programmed in the
application circuit. See the relevant Application
Note AN620.
Electronic Sign atur e
The Electronic Signature (ES) mode allows the
reading out of a binary code from an EPROM that
will identify its manufacturer an d type. This mode
is intended for use b y programmin g equipment to
automaticall y 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 M27C322. To activate the ES
mode, the programming equipment must force
11.5V to 12.5V on address line A9 of the
M27C322, 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 Signa ture mode.
Byte 0 (A0 = VIL) represents the manufacturer
code and byte 1 (A0 = VIH) the device identifier
code. For the STMicroelectronics M27C322, these
two identifier bytes are given in Table 4 and can be
read-out on outputs Q0 to Q7.
ERASU RE OPERAT ION ( appli es to UV E PROM)
The erasure characteristics of the M27C322 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 fluoresce nt lamps have
wavelengths in the 3000-400 0 Å range . Research
shows that constant exposure to room level fluo-
rescent lighting could erase a typical M 27C322 in
about 3 years, whi le it would take approximately 1
week to cause erasure when exposed to direct
sunlight. If t he M27C322 is to be expos ed to these
types of lighting conditi ons for extended periods of
time, it is suggested that opaque labels be put over
the M27C322 window to prevent unint entional era-
sure. The recommended erasure procedure for
M27C322 is exposure to short wave ultraviolet
light which has a wavelength of 2537 Å . The inte-
grated dose (i.e. UV intensi ty 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 M27C322
should be placed within 2.5cm (1 inch) of t he l amp
tubes during the erasure. Some lamps have a filter
on their tubes which should be removed before
erasure.
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