Functional Description
(Continued)
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
PGM input with V
PP
at 25V will program that 27C16 A low
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
verify may be performed with V
PP
at 25V V
PP
must be at
V
CC
except during programming and program verify
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 (i e UV
intensity
c
exposure time) for erasure should be a minimum
of 15W-sec cm
2
The erasure time with this dosage is ap-
proximately 21 minutes using an ultraviolet lamp with a
12 000
mW
cm
2
power rating The 27C16 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
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
careful decoupling of the devices The supply current I
CC
has three segments that are of interest to the system de-
signer the 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 0 1
mF
ce-
ramic capacitor be used on every device between V
CC
and
GND This should be a high frequency capacitor of low in-
herent inductance In addition a 4 7
mF
bulk electrolytic ca-
pacitor should be used between V
CC
and GND for each
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
Mode
Read
Standby
Program
Program Verify
Program Inhibit
Output Disable
CE PGM
(18)
V
IL
V
IH
Pulsed V
IL
to V
IH
V
IL
V
IL
X
OE
(20)
V
IL
Don’t Care
V
IH
V
IL
V
IH
V
IH
V
P
(21)
V
CC
V
CC
25
25
25
V
CC
V
CC
(24)
5
5
5
5
5
5
Outputs
(9 – 11 13 – 17)
D
OUT
Hi-Z
D
IN
D
OUT
Hi-Z
Hi-Z
7
NSC [ NATIONAL SEMICONDUCTOR ]
