27C512 datasheet(7/22 Pages) STMICROELECTRONICS

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M27C512

tion, a 4.7µF bulk electrolytic capacitor should be

used between VCC and VSS for every eight devic-

es. The bulk capacitor should be located near the

power supply connection point.The purpose of the

bulk capacitor is to overcome the voltage drop

caused by the inductive effects of PCB traces.

Figure 6. Programming Flowchart

Programming

When delivered (and after each erasure for UV

EPROM), all bits of the M27C512 are in the '1'

state. Data is introduced by selectively program-

ming '0's into the desired bit locations. Although

only '0's will be programmed, both '1's and '0's can

be present in the data word. The only way to

change a '0' to a '1' is by die exposure to ultraviolet

light (UV EPROM). The M27C512 is in the pro-

gramming mode when VPP input is at 12.75V and

E is pulsed to VIL. The data to be programmed is

applied to 8 bits in parallel to the data output pins.

The levels required for the address and data in-

puts are TTL. VCC is specified to be 6.25V ±

0.25V. The M27C512 can use PRESTO IIB Pro-

gramming Algorithm that drastically reduces the

programming time (typically less than 6 seconds).

Nevertheless to achieve compatibility with all pro-

gramming equipments, PRESTO Programming

Algorithm can be used as well.

PRESTO IIB Programming Algorithm

PRESTO IIB Programming Algorithm allows the

whole array to be programmed with a guaranteed

margin, in a typical time of 6.5 seconds. This can

be achieved with STMicroelectronics M27C512

due to several design innovations described in the

M27C512 datasheet to improve programming effi-

ciency and to provide adequate margin for reliabil-

ity. Before starting the programming the internal

MARGIN MODE circuit is set in order to guarantee

that each cell is programmed with enough margin.

Then a sequence of 100µs program pulses are ap-

plied to each byte until a correct verify occurs. No

overprogram pulses are applied since the verify in

MARGIN MODE provides the necessary margin.

Program Inhibit

Programming of multiple M27C512s in parallel

with different data is also easily accomplished. Ex-

cept for E, all like inputs including GVPP of the par-

allel M27C512 may be common. A TTL low level

pulse applied to a M27C512's E input, with VPP at

12.75V, will program that M27C512. A high level E

input inhibits the other M27C512s 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 G

at VIL. Data should be verified with tELQV after the

falling edge of E.

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 M27C512. To activate the ES

mode, the programming equipment must force

11.5V to 12.5V on address line A9 of the

M27C512. 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 Signa-

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

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

identifier

code.

For

the

STMicroelectronics

M27C512, these two identifier bytes are given in

Table 3. and can be read-out on outputs Q7 to Q0.

AI00738B

n = 0

Last

Addr

VERIFY

E = 100

µs Pulse

++n

= 25

++ Addr

VCC = 6.25V, VPP = 12.75V

FAIL

CHECK ALL BYTES

1st: VCC = 6V

2nd: VCC = 4.2V

YES

SET MARGIN MODE

RESET MARGIN MODE

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