Epson LQ-2550 Technical Manual page 258

EPROM, which is a ultra-violet erasable and electrically programmable ROM.
The 27256 is an
Features:
X 8 bits
32768 words
TTL compatible input/output
5
V single power supply
+
Access time: 250 nS (max.)
28 pins (DIP)
Terminal Functions:
AO to Al 4: Address input
o DO to D7: Data output
Program power supply
Power supply (+5 V)
V..:
Mode
Read
Output Disable
Standby
High Performance Program
—
P r o g r a m V e r i f y
O p t i o n a l V e r i f y
P r o g r a m I n h i b i t
Identifier
NOTES: 1.
X... Don't care
2. VH = 12.OV & 0.5V
o
o
Chip Enable
Y- Decode
-
Address
-
X - Decode
Figure A-1 3. 27256
Table A-5. 27256 Signal Status
—
I
I
' :
I
B l o c k D i a g r a m
OE A 9
L L
x
L
H x
H x
x
L x
H
H L
x
L
L x
H
H x
L VH
– 0 . 6 - + 7 V
3 .
4. – 0 . 6 - + 1 4 V
A-1 3
3
5
6
A3 7
8
9
o
10
11
G NO M,
Figure A-12. 27256 Pin Diagram
put
I
Y- Select
Memory
Mat rix
D out
High Z
High Z
D
D out
High Z
Code
Al 3
26
25 A a
23 Aft
21 A,IJ
19 D7
16 DG
17 05
16 D4
13 03
outputs
-
in