Radio Shack TRS-80 Operation Manual page 22
Ptc-64 printer controller
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Also See for TRS-80:
- Reference manual (274 pages) ,
- User manual (236 pages) ,
- Service manual (199 pages)
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•
the
first
two
bytes (27 39)
are the
REDEFINE
Control
Sequence
• nl
is
the character
to
be
redefined (144-159)
• n2
through
nX
are the
bytes
of information
for
specifying
the dots
to
be
printed
(more
on
this
later).
A
maximum
of
24
bytes of information
can
be
sent.
However,
if
less
than
24
bytes
are
used,
CHR$
(
127)
must
be
the
last
byte
sent.
When
the
REDEFINE
sequence
is
sent, the Printer
Controller automatically enters the
Graphics
Mode.
If
you want
to
use alpha-numeric
characters,
send
CHR$
(
30
)
as
the
first
character.
This
turns the
Graphics
Mode
off
and
you
may
then use regular characters
for redefinition
(this
will
be
explained
in
detail).
Redefining
a special
character consists primarily of
telling
the Printer exactly
what
dots
to
print.
To
understand
how
this
is
done,
you
should
first
be
aware
that
the
dot matrix
Print
Head
consists
of
a vertical
arrangement of "dots." Furthermore, each
dot has
its
own
"dot
number"
(see
illustration
below).
Another
important thing
you
should
know,
is
that
most
characters
are
formed
in
a
5x7
grid.
In other
words, each
character
is
made
up
of
dots
arranged
in
a space
of
5
columns
by
7 rows.
Every
dot
in
the grid
is
addressed
by
a
Dot
#
according
to
its
position within
each column.
The Dot
#s
correspond
exactly
to
the Print
Head
dot arrangement.
You
may
think of the
vertical
columns
as
bytes of information
making up
a
character.
See
the
illustration
below.
Dot
#s
(Dec.)
1st
Bytes
2nd
3rd
4th
5th
Dot
#
(Hex.)
1
1
2
2
4
4
8
8
16
10
32
20
64
40
To
tell
the printer
which
dots
to print,
you
should
add up
all
the
Dot
#s
in
each
column
of
the grid that
you wish
printed
and
then
add
128
to their
sum.
The
resulting
number
is
then
sent to the Printer Controller.
This
constitutes
one
byte of information.
By
successively repeating
this
process,
you
can
create
your
own
special characters.
The
general
procedure
to
redefine special characters
is:
1.
Send
the
REDEFINE
sequence
(27
39).
2.
Select the special character
to
be
redefined
(in
the
144
to
159
range).
14
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