Radio Shack 26-3801 Service Manual page 47

&3
PAo_
7
(
8
>
(Input/Output)
PB.-,(8)
(Input/Output)
PCo_
s
(6)
(Input/Output)
These
8 pins are general
purpose I/O
pins.
The
in/out direction
is
selected by programming
the
command
register.
These
8 pins are general
purpose I/O
pins.
The
in/out direction
is
selected
by programming
the
command
register.
These
6 pins
can function
as either input
port,
output
port, or
as control
signals for
PA
and
PB. Programming
is
done
through
the
command
register.
When PC _
s
are used
as
control
signals,
they
will
provide the following:
PC
- A INTR
(Port
A
Interrupt)
PC,
- ABF
(Port
A
Buffer
Full)
Pd - A
STB
(Port
A
Strobe)
PC
3
-
B
INTR
(Port
B
Interrupt)
PC
4
-
B
BF
(Port
B Buffer
Full)
PCs
-
B
STB
(Port
B
Strobe)
TIMER
IN
(Input)
Input
to
the counter-timer.
TIMER OUT
(Output)
Timer
output. This output can
be
either
a
square wave
or
a
pulse
depending on
the timer
mode.
Vcc
+5
volt supply.
Vss Ground
Reference.