Programming multiple 27C16s in parallel with the same data

can be easily accomplished due to the simplicity of the pro-

gramming requirements

Like inputs of the paralleled

27C16s may be connected together when they are pro-

grammed with the same data A high level TTL pulse ap-

plied to the CE PGM input programs the paralleled 27C16s

Program Inhibit

Programming multiple 27C16s in parallel with different data

is also easily accomplished Except for CE PGM all like

inputs (including OE) of the parallel 27C16s may be com-

mon A TTL level program pulse applied to an 27C16’s CE

level CE PGM input inhibits the other 27C16 from being

programmed

Program Verify

A verify should be performed on the programmed bits to

determine whether they were correctly programmed The

ERASURE CHARACTERISTICS

The erasure characteristics of the 27C16 are such that era-

sure begins to occur when exposed to light with wave-

lengths shorter than approximately 4000 Angstroms ( ) It

should be noted that sunlight and certain types of fluores-

cent lamps have wavelengths in the 3000 – 4000

range

Opaque labels should be placed over the 27C16 window to

prevent unintentional erasure Covering the window will also

prevent temporary functional failure due to the generation of

photo currents

The recommended erasure procedure for the 27C16 is ex-

posure to short wave ultraviolet light which has a wave-

length of 2537 Angstroms ( ) The integrated dose (ie UV

proximately 21 minutes using an ultraviolet lamp with a

within 1 inch of the lamp tubes during erasure Some lamps

have a filter on their tubes which should be removed before

erasure

Note

The 27C16-550 may take up to 60 minutes for complete erasure to

occur

An erasure system should be calibrated periodically The

distance from lamp to unit should be maintained at one inch

The erasure time increases as the square of the distance (If

distance is doubled the erasure time increases by a 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 Programmers components and even

system designs have been erroneously suspected when in-

complete erasure was the problem

SYSTEM CONSIDERATION

The power switching characteristics of EPROMs require

has three segments that are of interest to the system de-

signerthe standby current level the active current level

and the transient current peaks that are produced on the

falling and rising edges of chip enable The magnitude of

these transient current peaks is dependent on the output

capacitance loading of the device The associated transient

voltage peaks can be suppressed by properly selected de-

coupling capacitors It is recommended that a 01 mF ce-

GND This should be a high frequency capacitor of low in-

herent inductance In addition a 47 mF bulk electrolytic ca-

eight devices The bulk capacitor should be located near

where the power supply is connected to the array The pur-

pose of the bulk capacitor is to overcome the voltage drop

caused by the inductive effects of the PC board traces

TABLE I Mode Selection

Pins

CE PGM

OE

Outputs

Mode

(18)

(20)

(21)

(24)

(9 – 11 13 – 17)

Read

Standby

Don’t Care

5

Hi-Z

Program

25

5

Program Verify

25

5

Program Inhibit

25

5

Hi-Z

Output Disable

X

5

Hi-Z

7