27128 datasheet(3/10 Pages) STMICROELECTRONICS

3 / 10 page

For the most efficient use of these two control lines,

E should be decoded and used as the primary

device selecting function, while G should be 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 deselected memory devices

are in their low power standby mode and that the

output pins are only active when data is required

from a particular memory device.

System Considerations

The power switching characteristics of fast

EPROMs require careful decoupling of the devices.

The supply current, ICC, has three segments that

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 this 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 recommended that a 1

µF ceramic

capacitor be used on every device between VCC

and VSS. This should be a high frequency capacitor

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

between VCC and GND for every eight devices. The

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 for UV

EPPROM), all bits of the M27128A 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 present in the data word. The only way to

change a “0" to a ”1" is by ultraviolet light erasure.

The M27128A is in the programming mode when

VPP input is at 12.5V and E and P are at 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.

Fast Programming Algorithm

Fast Programming Algorithm rapidly programs

M27128A 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

Mode

PA9

VPP

Q0 - Q7

Read

VIL

VIH

XVCC

Data Out

Output Disable

VIL

VIH

XVCC

Hi-Z

Program

VIL

VIH

VIL Pulse

VPP

Data In

Verify

VIL

VIH

XVPP

Data Out

Program Inhibit

VIH

XXX

VPP

Hi-Z

Standby

VIH

XXX

VCC

Hi-Z

Electronic Signature

VIL

VIH

VID

VCC

Codes Out

Note: X = VIH or VIL, VID = 12V

± 0.5%.

Table 3. Operating Modes

Identifier

Hex Data

Manufacturer’s Code

VIL

00100

20h

Device Code

VIH

10001

89h

Table 4. Electronic Signature

DEVICE OPERATION (cont’d)

3/10

M27128A

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