The six modes of operation of the EPROM are listed in Table1. It
should be noted that all inputs for the six modes are at TTL levels.
The power supplies required are VCC and OE/VPP. The OE/VPP
power supply must be at 12.75V during the three programming
modes, and must be at 5V in the other three modes. The VCC
power supply must be at 6.5V during the three programming
modes, and at 5V in the other three modes.
The EPROM has two control functions, both of which must be
logically active in order to obtain data at the outputs. Chip Enable
(CE/PGM) is the power control and should be used for device
selection. Output Enable (OE/VPP) is the output control and should
be used to gate data to the output pins, independent of device
selection. Assuming that addresses are stable, address access
time (tACC) is equal to the delay from CE to output (tCE). Data is
available at the outputs tOE after the falling edge of OE, assuming
that CE has been low and addresses have been stable for at least
tACC – tOE.
The EPROM has a standby mode which reduces the active power
dissipation by over 99%, from 220 mW to 0.55 mW. The EPROM
is placed in the standby mode by applying a CMOS high signal to
the CE/PGM input. When in standby mode, the outputs are in a
high impedance state, independent of the OE input.
The EPROM is placed in output disable by applying a TTL high
signal to the OE input. When in output disable all circuitry is
enabled, except the outputs are in a high impedance state (TRI-
Because the EPROM is usually used in larger memory arrays,
Fairchild has provided a 2-line control function that accommo-
dates this use of multiple memory connections. The 2-line control
function allows for:
1. the lowest possible memory power dissipation, and
2. complete assurance that output bus contention will not
To most efficiently use these two control lines, it is recommended
that CE/PGM be decoded and used as the primary device select-
ing function, while OE/VPP be made a common connection to all
devices in the array and connected to the READ line from the
system control bus.
This assures that all deselected memory devices are in their low
power standby modes and that the output pins are active only
when data is desired from a particular memory device.
CAUTION: Exceeding 14V on pin 22 (OE/VPP) will damage the
Initially, and after each erasure, all bits of the EPROM are in the
“1’s” state. Data is introduced by selectively programming “0’s”
into the desired bit locations. Although only “0’s” will be pro-
grammed, both “1’s” and “0’s” can be presented in the data word.
The only way to change a “0” to a “1” is by ultraviolet light erasure.
The EPROM is in the programming mode when the OE/VPP is at
12.75V. It is required that at least a 0.1 µF capacitor be placed
across VCC to ground to suppress spurious voltage transients
which may damage the device. The data to be programmed is
applied 8 bits in parallel to the data output pins. The levels required
for the address and data inputs are TTL.
When the address and data are stable, an active low, TTL program
pulse is applied to the CE/PGM input. A program pulse must be
applied at each address location to be programmed.
The EPROM is programmed with the Turbo Programming Algo-
rithm shown in Figure 1. Each Address is programmed with a
series of 50 µs pulses until it verifies good, up to a maximum of 10
pulses. Most memory cells will program with a single 50 µs pulse.
(The standard National Semiconductor Algorithm may also be
used but it will have longer programming time.)
The EPROM must not be programmed with a DC signal applied to
the CE/PGM input.
Programming multiple EPROM in parallel with the same data can
be easily accomplished due to the simplicity of the programming
requirements. Like inputs of the parallel EPROM may be con-
nected together when they are programmed with the same data.
A low level TTL pulse applied to the CE/PGM input programs the
Programming multiple EPROMs in parallel with different data is
also easily accomplished. Except for CE/PGM all like inputs
(including OE/VPP) of the parallel EPROMs may be common. A
TTL low level program pulse applied to an EPROM’s CE/PGM
input with OE/VPP at 12.75V will program that EPROM. A TTL high
level CE/PGM input inhibits the other EPROMs from being pro-
A verify should be performed on the programmed bits to determine
whether they were correctly programmed. The verify is accom-
plished with OE/VPP and CE at VIL. Data should be verified TDV
after the falling edge of CE.
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
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 manufacturer and device type. The code for
NM27C512 is “8F85”, where “8F” designates that it is made by
Fairchild Semiconductor, and “85” designates a 512K part.
The code is accessed by applying 12V ±0.5V to address pin A9.
Addresses A1–A8, A10–A16, and all control pins