Radio Shack TRS-80 Operation Manual page 32

2.
BUSY
and
BUSY*
will
be
active for a
minimum
of
90 uS upon
receipt of a
STROBE
from
the
computer. This
may
not
be
disabled, but
may
be extended
by
turning
on
the
appropriate bits in Port
1
(Write).
Printer signals that
need
to
be monitored:
(Port
1
Read)
1.
BUSY
and
BUSY*...
If
BUSY
=
1
and
BUSY* =
then
the printer
is
ready
to
accept data (provided
there
is
no
printer
fault).
(See next paragraph.)
If
BUSY =
and
BUSY* =
1
then the printer cannot accept data.
2.
FAULT*
...This will indicate a printer fault
such
as Printer
Off
Line or ribbon end.
The
printer
cannot accept data in
this state.
3.
EMPTY
...
This
bit will
indicate
that
the printer
is
out of paper.
In
some
instances,
this
condition will also turn
on
the
FAULT
bit.
ACK*
byte.
This
bit
indicates that the printer
has received and processed the current
5.
PAUSE, COPY,
and
CLEAR
...
Indicate
which key
is
being
pressed.
You
should
look
at
these
in
your
interrupt service routine to
determine
which key was
pressed.
For
detailed
information
on programming
refer to a
Z-80 Assembly language manual.
I/O Port
Mapping
Port (Read)
This port
is
the
data port
from
the
computer. This
data
is
only guaranteed
valid for
2.5uS. Therefore,
it
should be read
early
in
the
NMI
service routine.
Port (Write)
This port
is
the data port
to
the
printer.
It
writes the data
to the printer
and
generates a
STROBE*.
Port
1
(Read)
Bit 7
—
CLEAR
key from
front panel.
Bit
6
—
COPY
key from
front panel.
Bit 5
Bit
4
Bit 3
Bit 2
Bit
1
BitO
—
PAUSE
key from
front panel.
—
BUSY*
from
printer
—
FAULT*
from
printer
—
BUSY
from
printer
—
EMPTY
from
printer
—
ACK*
from
printer
Port
1
(Write)
Bit
7
Bit
6
Bit 5
Bit
4
Bit 3
Bit 2
Bit
1
BitO
Status
LED
(see
Note
1)
Status
LED
(see
Note
1)
Piezo
Buzzer
Fault
LED
and
to
computer
BUSY*
to
computer
BUSY
to
computer
ACK*
to
computer
(see
Note
2)
EMPTY
to
computer
=
key
pressed
=
key
pressed
=
key
pressed
=
Printer
Busy
=
Fault
Condition
=
Printer
Busy
=
Out
of Paper
1
=
Byte Accepted
l=ON
=
Fault
Condition
=
Busy
1
=
Busy
=
Byte Accepted
1
=
Out of Paper
Notes:
24