NM27C128VE200 Ver la hoja de datos (PDF) - Fairchild Semiconductor

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NM27C128VE200

131,072-Bit (16K x 8) High Performance CMOS EPROM

Fairchild Semiconductor 

Functional Description (Continued)

Program Verify

A verify should be performed on the programmed bits to determine

whether they were correctly programmed. The verify may be

performed with VPP at 12.75V. VPP must be at VCC, except during

programming and program verify.

AFTER PROGRAMMING

Opaque labels should be placed over the EPROM window to

prevent unintentional erasure. Covering the window will also

prevent temporary functional failure due to the generation of photo

currents.

MANUFACTURER’S IDENTIFICATION CODE

The EPROM has a manufacturer’s identification code to aid in

programming. When the device is inserted in an EPROM pro-

grammer socket, the programmer reads the code and then

automatically calls up the specific programming algorithm for the

part. This automatic programming control is only possible with

programmers which have the capability of reading the code.

The Manufacturer’s Identification code, shown in Table 2, specifi-

cally identifies the manufacture and device type. The code for

NM27C128 is “8F83”, where “8F” designates that it is made by

Fairchild Semiconductor, and “83” designates a 128K part.

The code is accessed by applying 12V ±0.5V to address pin A9.

Addresses A1–A8, A10–A13, and all control pins are held at VIL.

Address pin A0 is held at VIL for the manufacturer’s code, and held

at VIH for the device code. The code is read on the eight data pins,

O0 –O7 . Proper code access is only guaranteed at 25°C to ±5°C.

ERASURE CHARACTERISTICS

The erasure characteristics of the device are such that erasure

begins to occur when exposed to light with wavelengths shorter

than approximately 4000 Angstroms (Å). It should be noted that

sunlight and certain types of fluorescent lamps have wavelengths

in the 3000Å – 4000Å range.

The recommended erasure procedure for the EPROM is expo-

sure to short wave ultraviolet light which has a wavelength of

2537Å. The integrated dose (i.e., UV intensity x exposure time) for

erasure should be a minimum of 15W-sec/cm2.

The EPROM should be placed within 1 inch of the lamp tubes

during erasure. Some lamps have a filter on their tubes which

should be removed before erasure. Table 1 shows the minimum

EPROM erasure time for various light intensities.

An erasure system should be calibrated periodically. The distance

from lamp to device should be maintained at one inch. The erasure

time increases as the square of the distance from the lamp (if

distance is doubled the erasure time increases by factor of 4).

Lamps lose intensity as they age. When a lamp is changed, the

distance has changed, or the lamp has aged, the system should

be checked to make certain full erasure is occurring. Incomplete

erasure will cause symptoms that can be misleading. Program-

mers, components, and even system designs have been errone-

ously suspected when incomplete erasure was the problem.

SYSTEM CONSIDERATION

The power switching characteristics of EPROMs require careful

decoupling of the devices. The supply current, ICC, has three

segments that are of interest to the system designer: the standby

current level, the active current level, and the transient current

peaks that are produced by voltage transitions on input pins. The

magnitude of these transient current peaks is dependent of the

output capacitance loading of the device. The associated VCC

transient voltage peaks can be suppressed by properly selected

decoupling capacitors. It is recommended that at least a 0.1 µF

ceramic capacitor be used on every device between VCC and

GND. This should be a high frequency capacitor of low inherent

inductance. In addition, at least a 4.7 µF bulk electrolytic capacitor

should be used between VCC and GND for each eight devices. The

bulk capacitor should be located near where the power supply is

connected to the array. The purpose of the bulk capacitor is to

overcome the voltage drop caused by the inductive effects of the

PC board traces.

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