Figure 7. Programming and Verify Modes AC Waveforms
M27C801
A0-A19
Q0-Q7
VCC
GVPP
E
tAVEL
DATA IN
tQVEL
VALID
tEHQX
DATA OUT
tEHAX
tEHQZ
tVCHEL
tEHVPX
tELQV
tVPHEL
tVPLEL
tELEH
PROGRAM
VERIFY
AI01270
Figure 8. Programming Flowchart
VCC = 6.25V, VPP = 12.75V
SET MARGIN MODE
n=0
NO
++n
= 25
YES
E = 50µs Pulse
NO
VERIFY
YES
++ Addr
FAIL
Last NO
Addr
YES
RESET MARGIN MODE
CHECK ALL BYTES
1st: VCC = 6V
2nd: VCC = 4.2V
AI01271B
PRESTO IIB Programming Algorithm
PRESTO IIB Programming Algorithm allows the
whole array to be programmed with a guaranteed
margin, in a typical time of 52.5 seconds. This can
be achieved with STMicroelectronics M27C801
due to several design innovations to improve pro-
gramming efficiency and to provide adequate mar-
gin for reliability. Before starting the programming
the internal MARGIN MODE circuit is set in order
to guarantee that each cell is programmed with
enough margin. Then a sequence of 50µs pro-
gram pulses are applied to each byte until a cor-
rect verify occurs. No overprogram pulses are
applied since the verify in MARGIN MODE pro-
vides the necessary margin.
Program Inhibit
Programming of multiple M27C801s in parallel
with different data is also easily accomplished. Ex-
cept for E, all like inputs including GVPP of the par-
allel M27C801 may be common. A TTL low level
pulse applied to a M27C801's E input, with VPP at
12.75V, will program that M27C801. A high level E
input inhibits the other M27C801s 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
at VIL. Data should be verified with tELQV after the
falling edge of E.
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