NM27C128N120 Ver la hoja de datos (PDF) - Fairchild Semiconductor
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NM27C128N120 Datasheet PDF : 11 Pages
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Functional Description
DEVICE OPERATION
The six modes of operation of the EPROM are listed in Table 1. It
should be noted that all inputs for the six modes are at TTL levels.
The power supplies required are VCC and VPP. The 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.
Read Mode
The EPROM has two control functions, both of which must be
logically active in order to obtain data at the outputs. Chip Enable
(CE) is the power control and should be used for device selection.
Output Enable (OE) 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.
Standby Mode
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 input. When in standby mode, the outputs are in a high
impedance state, independent of the OE input.
Output Disable
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-
STATE).
Output OR-Typing
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
occur.
To most efficiently use these two control lines, it is recommended
that CE be decoded and used as the primary device selecting
function, while OE 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.
Programming
CAUTION: Exceeding 14V on pin 1 (VPP) will damage the EPROM.
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 VPP power
supply is at 12.75V, CE is at VIL, and OE is at VIH. It is required that
at least a 0.1 µF capacitor be placed across VPP, 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 PGM input. A program pulse must be
applied at each address location to be programmed. The EPROM
is programmed with the Turbo Programming Algorithm 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 PGM input.
Programming multiple EPROM in parallel with the same data can
be easily accomplished due to the simplicity of the programming
requirments. Like inputs of the parallel EPROM may be connected
together when they are programmed with the same data. A low
level TTL pulse applied to the PGM input programs the paralleled
EPROM.
Program Inhibit
Programming multiple EPROMs in parallel with different data is
also easily accomplished. Except for CE all like inputs (including
OE) of the parallel EPROMs may be common. A TTL low level
program pulse applied to an EPROM’s CE input with VPP at
12.75V will program that EPROM. A TTL high level CE input
inhibits the other EPROMs from being programmed.
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