For the most efficient use of these two control lines,

E should be decoded and used as the primary

made a common connection to all devices in the

array and connected to the READ line from the

system control bus. This ensures that all dese-

lected memory devices are in their low power

standby mode and that the output pins are only

active when data is required from a particular mem-

ory device.

System Considerations

The power switching characteristics of fast

EPROMs require careful decoupling of the devices.

are of interest to the system designer : the standby

current level, the active current level, and transient

current peaks that are produced by the falling and

rising edges of E. The magnitude of the transient

current peaks is dependent on the capacitive and

inductive loading of the device at the output. The

associated transient voltage peaks can be sup-

pressed by complying with the two line output

control and by properly selected decoupling ca-

pacitors. It is recommenced that a 1

µF ceramic

of low inherent inductance and should be placed

as close to the device as possible. In addition, a

4.7

µF bulk electrolytic capacitor should be used

bulk capacitor should be located near the power

supply connection point. The purpose of the bulk

capacitor is to overcome the voltage drop caused

by the inductive effects of PCB traces.

Programming

When delivered, and after each erasure, all bits of

the M27512 are in the “1" state. Data is introduced

by selectively programming ”0s" into the desired bit

locations. Although only “0s” will be programmed,

both “1s” and “0s” can be present in the data word.

The only way to change a “0" to a ”1" is by ultraviolet

light erasure. The M27512 is in the programming

TTL-low. 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.

The M27512 can use PRESTO Programming Algo-

rithm that drastically reduces the programming

time (typically less than 50 seconds). Nevertheless

to achieve compatibility with all programming

equipment, the standard Fast Programming Algo-

rithm may also be used.

Fast Programming Algorithm

Fast Programming Algorithm rapidly programs

M27512 EPROMs using an efficient and reliable

method suited to the production programming en-

vironment. Programming reliability is also ensured

as the incremental program margin of each byte is

continually monitored to determine when it has

been successfully programmed. A flowchart of the

M27512 Fast Programming Algorithm is shown in

Figure 8.

Mode

E

A9

Q0 - Q7

Read

X

Data Out

Output Disable

X

Hi-Z

Program

X

Data In

Verify

X

Data Out

Program Inhibit

X

Hi-Z

Standby

X

X

Hi-Z

Electronic Signature

Codes

± 0.5%.

Table 3. Operating Modes

Identifier

A0

Q7

Q6

Q5

Q4

Q3

Q2

Q1

Q0

Hex Data

Manufacturer’s Code

00100

00

0

20h

Device Code

00001

10

1

0Dh

Table 4. Electronic Signature

DEVICE OPERATION (cont’d)

M27512

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