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NTE2708

Integrated Circuit NMOS, 8K UV EPROM, 450ns

NTE Electronics 

Operation (Read Mode):

Address (A0–A9)

The address–valid interval determines the device cycle time. The 10–bit positive–logic address is

decoded on–chip to select one of the 1024 words of 8–bit length in the memory array. A0 is the least–

significant bit and A9 is the most–significant bit of the words address.

Chip Select, Program Enable [CS (PE)]

When the chip select is low, all eight outputs are enabled and the eight–bit addressed word can be

read. When the chip select is high, all eight outputs are in a high–impedance state.

Data Out (Q1–Q8)

The chip must be selected before the eight–bit outputs word can be read. Data will remain valid until

the address is changed or the chip is deselected. When deselected, the three–state outputs are in

a high–impedance state. The outputs will drive TTL circuits without external components.

Program

The program pin must be held below VCC in the read mode.

Operation (Program Mode):

Erase

Before programming, the NTE2708 is erased by exposing the chip through the transparent lid to high–

intensity ultraviolet light (wavelength 2537 angstroms). The recommended minimum exposure dose

(= UV intensity x exposure time) is fifteen watt–seconds per square centimeter. Thus, a typical 12

milliwatt per square centimeter, filterless UV lamp will erase the device in a minimum of 21 minutes.

The lamp should be located about 2.5 centimeters above the chip during erasure. After erasure, all

bits are in the “1” state.

Programming

Programming consists of successively depositing a small amount of charge to a selected memory cell

that is to be changed from the erased high state to the low state. A low can be changed to a high only

by erasure. Programming is normally accomplished on a PROM or EPROM Programmer. Program-

ming must be done at room temperature (+25°C) only.

To Start Programming

First bring the CS (PE) pin to +12V to disable the outputs and convert them to inputs. This pin is held

high for the duration of the programming sequence. The first word to be programmed is addressed

(it is customary to begin with the “0” address) and the data to be stored is placed on the Q1–Q8 pro-

gram inputs. Then a +25V program pulse is applied to the program pin. After 0.1 to 1.0 milliseconds

the program pin is brought back to 0V. After at least one microsecond the word address is sequentially

changed to the next location, the new data is set up and the program pulse is applied.

Programming continues in this manner until all words have been programmed. This constitutes one

of N program loop. The entire sequence is then repeated N times with N x tw(PR) ≥ 100 ms. Thus,

if tw(PR) = 1 ms; then N = 100, the minimum number of program loops required to program the EPROM.

To Stop Programming

After cycling through the N program loops, the last program pulse is brought to 0V, then Program En-

able [CS (PE)] is brought to VIL which takes the device out of the program mode. The data supplied

by the programmer must be removed before the address is changed since the program inputs are now

data outputs and change of address could cause a voltage conflict on the output buffer. Q1–Q8 out-

puts are invalid up to 10 microseconds after the program enable pin is brought from VIH(PE) to VIL.

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