5.2.4
8254 & interrupt
VCC
C5
10u
C1210
J2
CON20A
JDIP20P
C1
.1u
C0805
J1
CON20A
JDIP20P
1
3
5
7
9
11
13
15
17
19
2
4
6
8
10
12
14
16
18
20
U1
74HCT138
SOIC16
1
2
3
6
4
5
15
14
13
12
11
10
9
7
A
B
C
G1
G2A
G2B
Y0
Y1
Y2
Y3
Y4
Y5
Y6
Y7
U2
8254 PLCC
PLCC28
9
8
7
6
5
4
3
2
26
27
22
23
24
10
13
12
18
17
16
21
19
20
D0
D1
D2
D3
D4
D5
D6
D7
RD
WR
A0
A1
CS
CLK0
G0
OUT0
CLK1
G1
OUT1
CLK2
G2
OUT2
C2
.1u
C0805
GND
GND
GND
INT0
SCLK
INT1
VCC=28
GND=14
VCC=16
GND=8
+
WR\
RD\
TO_1
A0
A1
A2
A3
A4
CS\
The addressing space of 8254 is from BASE+0 to BASE+3 as follows:
Timer/Counter_0
BASE+0
Timer/Counter_1
BASE+1
Timer/Counter_2
BASE+2
Control word
BASE+3
The power-up default value of BASE is 0.
It is
not
recommended to change the value of BASE from 0 to another value.
I/O Expansion Bus for 7188X/7188E User’s Manual, Jan/2005 v1.5, 7PH-000-15---28