8

www.fairchildsemi.com

www.fairchildsemi.com

FM27C512

Functional Description (Continued)

are held at V

eight data pins, O0 –O 7 . Proper code access is only guaranteed

at 25

°C ±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

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

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, I

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 on the

output capacitance loading of the device. The associated V

CC

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 V

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 V

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.

Mode Selection

The modes of operation of the FM27C512 are listed in Table 1. A single 5V power supply is required in the read mode. All inputs are TTL

TABLE 1. Mode Selection

Pins

CE/PGM

OE/V

PP

V

CC

Outputs

Mode

Read

V

IL

V

IL

5.0V

D

OUT

Output Disable

X (Note 13)

V

IH

5.0V

High Z

Standby

V

IH

X

5.0V

High Z

Programming

V

IL

12.75V

6.25V

D

IN

Program Verify

V

IL

V

IL

6.25V

D

OUT

Program Inhibit

V

IH

12.75V

6.25V

High Z

TABLE 2. Manufacturer’s Identification Code

Pins

A0

A9

07

06

05

04

03

02

01

00

Hex

(10)

(24)

(19)

(18)

(17)

(16)

(15)

(13)

(12)

(11)

Data

Manufacturer Code

V

IL

12V

10001111

8F

Device Code

12V

10000101

85