M87C257 STMICROELECTRONICS [STMicroelectronics], M87C257 Datasheet - Page 3

• Manufacturer Part Number: M87C257
• Description: ADDRESS LATCHED 256K 32K x 8 UV EPROM and OTP EPROM
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Table 3. Operating Modes
Note: X = V
Table 4. Electronic Signature
be used to gate data to the output pins, inde-
pendent of device selection. Assuming that the
addresses are stable (AS = V
V
delay from E to output (t
the output after delay of t
of G, assuming that E has been low and the ad-
dresses have been stable for at least t
The M87C257 reduces the hardware interface in
multiplexed address-data bus systems. The proc-
essor multiplexed bus (AD0-AD7) may be tied to
the M87C257’s address and data pins. No sepa-
rate address latch is needed because the
M87C257 latches all address inputs when AS is
low.
Standby Mode
The M87C257 has a standby mode which reduces
the active current from 30mA to 100 A (Address
Stable). The M87C257 is placed in the standby
mode by applying a CMOS high signal to the E
input. When in the standby mode, the outputs are
in a high impedance state, independent of the G
input.
Manufacturer’s Code
Device Code
IL
Read (Latched Address)
Read (Applied Address)
Output Disable
Program
Verify
Program Inhibit
Standby
Electronic Signature
), the address access time (t
Identifier
IH
Mode
or V
IL
, V
ID
= 12V
ELQV
V
A0
V
0.5V
GLQV
IH
IL
). Data is available at
V
from the falling edge
IH
AVQV
IL
) or latched (AS =
Q7
V
V
V
V
V
V
V
Pulse
0
1
E
IH
IH
IH
IL
IL
IL
IL
) is equal to the
AVQV
Q6
0
0
-t
GLQV
Q5
V
V
V
V
V
V
V
G
X
1
0
.
IH
IH
IH
IL
IL
IL
IL
Two Line Output Control
Because EPROMs are usually used in larger mem-
ory arrays, this product features a 2 line control
function which accommodates the use of multiple
memory connection. The two line control function
allows:
a. the lowest possible memory power dissipation,
b. complete assurance that output bus contention
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 mem-
ory devices are in their low power standby mode
and that the output pins are only active when data
is desired from a particular memory device.
Q4
0
0
will not occur.
Q3
V
A9
0
0
X
X
X
X
X
X
X
ID
Q2
0
0
ASV
V
V
V
Q1
V
V
V
0
0
X
X
PP
PP
PP
IH
IL
IL
PP
Q0
0
0
Data Out
Data Out
Data Out
Q0 - Q7
Data In
M87C257
Codes
Hex Data
Hi-Z
Hi-Z
Hi-Z
20h
80h
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