General Description; Printer Operation; Basic Block Diagram; Paper Motion - Radio Shack TRS-80 Service Manual

1.1
GENERAL
DESCRIPTION
(Figure
1-1)
The
printers
shown
in
Figure
1-1 are
60
character-per-second,
uni-directional
impact
printers
with an effective
throughput
of
21 to
90
lines
per
minute
at
10 characters per inch;
and up
to
132 columns
of operator variable
density (10 to 16.5 characters
per inch).
The
pinch
roller
(26-1150) unit prints
in
8
inch lengths
on
roll
paper
up
to 9.8 inches
(250
mm)
wide, while the
tractor drive
model
(26-1152) prints
in
8 inch lengths
on paper
12.1
inches (307
mm)
wide.
PINCH
ROLLER
(26-1150)
TRACTOR FEED
(26-1152)
Figure
1-1.
LINE
PRINTERS
Characters
are
formed
in a
5x7
dot matrix.
In
addition to the standard ASCII,
a
variety
of character
sets
give great flexibility
in
character formation.
The
printer will
accommodate up
to
64
characters.
All
the
electronics,
including logic driver circuits
and power
supplies, are
contained on
a single
printed circuit
board.
1.2
PRINTER OPERATION
The
printer
contains
a line
buffer
which
allows parallel
data to be
received at rates
up to 75,000 characters per second.
A
basic
block diagram of the
printer
is
shown
in
Figure 1-2.
CONTROL
PANEL
t
CONTROL
1.
PRINT
COMMAND
(CROR LAST CHAR.
1
2.
PAPER
MOVEMENT
(LINE
FEED)
3.
SPECIAL
FUNCTIONS
(MOTOR CONTROLI
HEAD MOTION CONTROL
CARRIAGE
ACTIVATOR
SOLENOIDS
DATA
PAPER
MOTION CONTROL
LINE
FEED
SOLENOID
INPUT
TIMING
*
LINE
BUFFER
CHARACTER
GENERATOR
WRITE
PRINT
HEAD
PULSES
Figure
1-2.
BASIC
BLOCK
DIAGRAM
Basically,
all
printer
functions can be
grouped
into
one
of
two
categories:
(1)
character printing,
and
(2)
paper motion.
1-1