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APPLICATION EXAMPLES
+5V
GND
Cl"
I"
Vee
VDD
Vss
27
2
P10
28
~
XTAL
1
P11
P12
29
~
P13
30
3
1
•
XTAL
2
P14
31
P15
32
P16
33
f----!
RESET
P17
34
I/O
P20
21
EA
P21
22
8049
23
8048
P22
24
-=
5
8748
P23
35
NC-
ss
8035'
P24
36
8039'
P25
3L-
P26
P27
38
+5V GND
PAO
PA1
PA2
1
12
{-
TO
DBO
DB1
13
39
INPUTS
::=!
T1
DB2
14
DB3
15
INT
DB4
16
DB5
17
DB6
18
DB7
19
ALE
PSEN
PROG
WR
RD
12
ADO
13 AD1
14
AD2
15
AD3
16
AD4
17
AD5
8155
18 AD6
19
AD7
256 x 8
RAM
PA3
PA4
PA5
PA6
PA7
PCO
PC1
PC2
PC3
11
8
10/M
PC4
9
RD
PC5
10
PBO
.
WR
PB1
11
PB2
ALE
PB3
r
ce
CAN
BE
SUPPLIED BY SYSTEM - 4 RESET TIMER TIMER
RESET
OR
PORT LINE
OF
8048 OUT IN
'EA
= 5V FOR 8035/8039
PB4
PB5
PB6
PBl
3
TIMER
• Both 1/0 and RAM are addressed
as
data memory
• Writing a bit to P27 determines whether RAM or 1/0
is
to
be accessed
ADDING A DATA MEMORY AND
I/O
EXPANDER
5-9
21
22
23
24
25
26
27
28
37
38
39
1
I/O
2
5
29
30
31
32
33
34
35
36