M27C320

10/15

PRESTO III Programming Algorithm

The PRESTO III Programming Algorithm allows

the whole array to be programed with a guaran-

teed margin in a typical time of 100 seconds. Pro-

gramming with PRESTO III consists of applying a

sequence of 50

µs program pulses to each word

until a correct verify occurs (see Figure 10). During

programing and verify operation a MARGIN

MODE circuit is automatically activated to guaran-

tee that each cell is programed with enough mar-

gin. No overprogram pulse is applied since the

verify in MARGIN MODE provides the neccessary

margin to each programmed cell.

Program Inhibit

Programming of multiple M27C320s in parallel

with different data is also easily accomplished. Ex-

cept for E, all like inputs including G of the parallel

M27C320 may be common. A TTL low level pulse

will program that M27C320. A high level E input in-

hibits the other M27C320s from being pro-

grammed.

Program Verify

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

grammed bits to determine that they were correct-

ly programmed. The verify is accomplished with G

falling edge of E.

Figure 9. Programming and Verify Modes AC Waveforms

tAVEL

VALID

AI02205

A0-A20

Q0-Q15

VCC

DATA IN

DATA OUT

E

tQVEL

tVCHEL

tVPHEL

tEHQX

tEHVPX

tELQV

tELEH

tEHQZ

tVPLEL

PROGRAM

VERIFY

GVPP

tEHAX

Figure 10. Programming Flowchart

AI02220

n= 0

Last

Addr

VERIFY

E= 50

µs Pulse

++n

=25

++ Addr

VCC = 6.25V, VPP = 12V

FAIL

CHECK ALL WORDS

BYTE = VIH

1st: VCC =6V

2nd: VCC = 4.2V

YES

NO

YES

NO

YES

NO

SET MARGIN MODE