
22
•
Control Programming
For example, If you defined the PET-48DIO's I/O port address as
300H, then the
index select register is
300H
, and
Data Read/Write
register is
301H
.
The relationship of ports' index select and ports' data read / write
shows a s figure.
The following table is ports' index that set by first I/O address.
PORT SELECT
INDEX
Description
GROUP #0 PA0
0H
EMULATE AS 8255 PA
GROUP #0 PB0
1H
EMULATE AS 8255 PB
GROUP #0 PC0
2H
EMULATE AS 8255 PC
CONTROL WORD of GROUP
#0
3H
EMULATE AS 8255 CW
GROUP #1 PA1
4H
EMULATE AS 8255 PA
GROUP #1 PB1
5H
EMULATE AS 8255 PB
GROUP #1 PC1
6H
EMULATE AS 8255 PC
CONTROL WORD of GROUP
#1
7H
EMULATE AS 8255 CW
COUNT1 OF 8253
80H
EVENT COUNTER
TIMER 1 OF 8253
81H
TIMER1 CASCADE WITH
TIMER2
TIMER 2 OF 8253
82H
TIMER2 CASCADE WITH
TIMER1
8253 CONTROL WORD
83H
Control Word for 8253
Table 3.2 Ports' index table