TLD10329 – 4

Note

All times shown in parentheses are minimum and in ms unless otherwise specified

Note 1

National’s standard product warranty applies only to devices programmed to specifications described herein

Note 2

Note 3

which may damage the device

Functional Description

DEVICE OPERATION

The six modes of operation of the 27C16 are listed in Table

I It should be noted that all inputs for the six modes are at

programming modes and must be at 5V in the other three

modes

Read Mode

The 27C16 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 indepen-

dent of device selection Assuming that addresses are sta-

the falling edge of OE assuming that CE has been low and

27C16 requires one address transition after initial power-up

to reset the outputs

Standby Mode

The 27C16 has a standby mode which reduces the active

power dissipation by 98% from 2625 mW to 053 mW The

27C16 is placed in the standby mode by applying a TTL high

signal to the CE input When in standby mode the outputs

are in a high impedance state independent of the OE input

Output OR-Tying

Because 27C16s are usually used in larger memory arrays

National has provided a 2-line control function that accom-

modates this use of multiple memory connections The

2-line control function allows for

a) the lowest possible memory power dissipation and

b) complete assurance that output bus contention will not

occur

To most efficiently use these two control lines it is recom-

mended that CE (pin 18) be decoded and used as the pri-

mary device selecting function while OE (pin 20) be made a

common connection to all devices in the array and connect-

ed to the READ line from the system control bus This as-

sures 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

27C16

Initially and after each erasure all bits of the 27C16 are in

the ‘‘1’’ state Data is introduced by selectively program-

ming ‘‘0s’’ into the desired bit locations Although only ‘‘0s’’

will be programmed both ‘‘1s’’ and ‘‘0s’’ can be presented

in the data word The only way to change a ‘‘0’’ to a ‘‘1’’ is

by ultraviolet light erasure

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 a 50 ms active high

TTL program pulse is applied to the CE PGM input A pro-

gram pulse must be applied at each address location to be

programmed You can program any location at any time

either individually sequentially or at random The program

pulse has a maximum width of 55 ms The 27C16 must not

be programmed with a DC signal applied to the CE PGM

input

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