Programming

When delivered (and after each erasure for UV

EPROM), all bits of the M27C64A are in the "1"

state. Data is introduced by selectively program-

ming "0"s into the desired bit locations. Although

only "0"s will be programmed, both "1"s and "0"s

can be present in the data word. The only way to

change a "0" to a "1" is by die exposition to ultra-

violet light (UV EPROM). The M27C64A is in the

programming mode when Vpp input is at 12.5V, E

is at VIL and P is pulsed to VIL. The data to be

programmed is applied to 8 bits in parallel to the

data output pins. The levels required for the ad-

dress and data inputs are TTL. VCC is specified to

be 6V

± 0.25V.

High Speed Programming

The high speed programming algorithm, described

in the flowchart, rapidly programs the M27C64A

using an efficient and reliable method, particularly

suited to the production programming environ-

ment. An individual device will take around 1 minute

to program.

Program Inhibit

Programming of multiple M27C64A in parallel with

different data is also easily accomplished. Except

for E, all like inputs including G of the parallel

M27C64A may be common. A TTL low level pulse

applied to a M27C64A P input, with E low and VPP

at 12.5V, will program that M27C64A. A high level

E input inhibits the other M27C64A from being

programmed.

Program Verify

A verify (read) should be performed on the pro-

grammed bits to determine that they were correctly

programmed. The verify is accomplished with E

and G at VIL, P at VIH, VPP at 12.5V and VCC at 6V.

Electronic Signature

The Electronic Signature (ES) mode allows the

reading out of a binary code from an EPROM that

will identify its manufacturer and type. This mode

is intended for use by programming equipment to

automatically match the device to be programmed

with its corresponding programming algorithm. The

ES mode is functional in the 25

°C ± 5°C ambient

temperature range that is required when program-

ming the M27C64A. To activate the ES mode, the

programming equipment must force 11.5V to 12.5V

on address line A9 of the M27C64A, with

VPP=VCC=5V. Two identifier bytes may then be

sequenced from the device outputs by toggling

address line A0 from VIL to VIH. All other address

lines must be held at VIL during Electronic Signa-

ture mode.

Byte 0 (A0=VIL) represents the manufacturer code

and byte 1 (A0=VIH) the device identifier code. For

the STMicroelectronics M27C64A, these two iden-

tifier bytes are given in Table 4 and can be read-out

on outputs Q0 to Q7.

4/12

M27C64A