Commodore 1526 User manual

SERVICE
MANUAL
1526
•
MPS
802 • 4023
PRINTERS
APRIL
1985 PN—31400303
Commodore Business
Machines, Inc.
1200
Wilson
Drive,
West
Chester,
Pennsylvania 19380
U.S.A.
Commodore
makes
no
expressed
or implied
war
ranties
with
regard
to the
information
contained
herein. The
information
is
made
available
solely on
an
as
is
basis, and
the
entire
risk
as to
quality
and
accuracy
is
with
the
user. Commodore
shall
not
be
liable for
any consequential
or
incidental
damages
in connection
with the
use of
the information con
tained
herein.
The listing of
any available replace
ment
part herein
does
not
constitute
in any
case
a
recommendation,
warranty
or
guaranty
as
to
quality
or
suitability
of
such replacement
part.
Reproduction
or
use
without
expressed permission,
of
editorial
or
pictorial
content,
in any
matter
is
prohibited.
This
manual contains
copyrighted
and
proprietary
information.
No
part
of
this
publication
may
be
reproduced, stored
in
a retrieval system,
or
transmitted
in
any
form or
by
any
means,
electronic,
mechanical,
photocopying,
recording
or
otherwise,
without the
prior
written
permis
sian of Commodore
Eiectronics
Limited.
Copyright
©
1985 by
Commodore Electronics Limited.
All
rights
reserved.

CONTENTS
Title
Page
SPECIFICATIONS
1
SET UP
AND TESTING
RIBBON
CARTRIDGE
2
PAPER INSTALLATION
3
SELF
TEST
4
ACCESSORIES
PARTS
LIST
5
MAINTENANCE
5
FUNCTIONAL
BLOCK
DIAGRAM
6
CIRCUIT
ThEORY
POWER
SUPPLY
7
RESET
LOGIC
8
CLOCK
CIRCUIT
9
MICROPROCESSOR
LOGIC
10
PAPER
FEED
MOTOR
11
CARRIAGE
MOTOR
12
PRINT
WIRE
DRIVE
13
PRINT
WIRE
COIL
PROTECTION
14
PAPER
CONTROL
LOGIC
15
CARRIAGE
POSITION
AND
HOME
SENSOR
16
1526
•
MPS
802
INTERFACE
LOGIC
17
4023
INTERFACE
LOGIC
18
TROUBLESHOOTING
GUIDES
19
PCB PARTS
LIST
22
ROMUPCRIDES
24
1526
•
:i,IPS
802
SCHEMATIC
24
DEVICE
NUMBER
CHANGE
25
4023
SCHEMATIC
25
MECHANiCAL
ADJUSTMENTS
HEAD
SHIFT
LEVER
26
PRINT
HEAD
26
HOME
SENSOR
27
WIRING
DIAGRAM
28
MECHANICAL
DISASSEMBLY
29
ASSEMBLY
NOTES
36
CASE
WORK’POWER
SUPPLY
37
MECHANICAL
ASSEMBLIES
38

SPECIFICATIONS
•
1526
•
MPS
802
•
4023.
PRINT
METHOD
•
Bi-directional
impact dot
matrix
CHARACTER
MATRIX
• 8
X
8
Dot Matrix
CHARACTERS
• Upper
&
lower
case letters
with
true
descenders.
Numerals
&
symbols.
All
PET
graphic
characters
GRAPHICS
•
8
Vertical
dots
—
maximum
640 columns
CHARACTER CODES
•
CBM
ASCII
code
PRINT
SPEED
•
60
CPS
MAXIMUM COLUMNS
•
80
Columns
LINE FEED
SPACING
• 6
Lines/inch
in character
mode
• 9
Lines/inch
in graphics
mode
LINE
FEED
SPEED
•
5
Lines/sec
in
character
mode
•
75
Lines/sec
in
graphics
mode
PAPER
FEED
•
Pin
feed
PAPER
WIDTH
•
45
to
10”
Width
(including
tractor
feed
holes>
• 85” Width
(after
tractor
holes>
MULTIPLE
COPIES
•
Original
plus
maximum
of
3
copies
POWER
REQUIREMENTS
• 120
Volts
AC,
60
Hz,
1.5
Amp
• 15261MPS
802
••
4023
•
INTERFACE
•
SERIAL
INTERFACE
•
IEEE
Protocol
COMPUTERS
• VIC2O,
C64,
COMPUTERS
• 4032,
8032,
SX64, C16,
8096,
SP9000,
PLUS
4
B-MODEL

SET
UP
AND
TESTING
VISUAL
OBSERVATION
is
particularly
important
before
attempting
to repair
a
printer.
Always
check
for
physical
damage
to the
mechanism.
Remove any
loose debris
that
may
have
accumulated
inside
the
unit.
Ribbon
Cartridge
PRINT
HEADfi
J(
RIBBON
CARTRIDGE
Before
installing
the
ribbon
cartridge, turn
the
printer
off.
By
carefully
pushing
the
carriage,
position
the
print
head
in
the
center
of
the
unit.
Turn
the
dial
knob
on
the
cartridge
in
the
direction
of
the
arrow
until
the
ribbon
is
taut.
Insert
the
cartridge
in
the
hooks
provided
and
push
down.
The
ribbon
must
be positioned
between
the
print
head
and
the
ribbon
guide.
CAUTION!
When installing
or
removing
the
ribbon
cartridge,
do
not
touch
the
FPC
cable.
Check
that
the
FPC
cable
remains
in
the
down
position as
shown.
FPC
CABLE
FPC
2

SET
UP
AND
TESTING
(Continued)
Paper Installation
To
install
paper, turn
the
printer
off,
remove
the
paper
rack
and
lift
the soundproof
cover.
Lift
the
paper
hold
down
shaft
and
raise
the
covers
of
the left
and
right
tractors
to
allow
access
to
the tractor
pins.
Align
the
paper
perforations
with
the
tractor
pins
and
close
the
covers,
The
left
tractor
assembly
must
be firmly
pressed
against the
left
stopper.
The
right
tractor
assembly
slides
to allow
adjustment
for
paper
width.
Once
the paper
is
aligned
in
the tractor,
turn
the
manual
feed
knob
while
guiding
the
paper
to
its
posi
tion behind
the
platen
(See
the paper
path
figure
below).
Standard
paper
may
be
used
by simply
in
stalling
it
in
front
of
the tractor
and
behind
the
platen,
using
the
manual
feed
knob
to
friction
feed
the paper.
TRACTOR
PIN
PA
TRACTOR
PLATEN
TRACTOR.
PAPER
HOLD-DOWN
SHAFT
PAPER
3

SET
UP
AND
TESTING
(Continued)
Self
Test
This
unit
has
a
pre-programmed
self-checking capability.
The
program
may be
used
to test
the
print
head
operation,
print
quality and
printer
mechanism
(ribbon feed
function,
linefeed,
etc).
The
self-test
function
is
initiated
by pressing
the paper
advance
switch
while
turning
on
the
power
supply
switch.
NOTE:
Do
not operate
the
self-test
function
in
the
no-paper
condition.
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SAMPLE
SELF
TEST
PRINT-OUT
Additional
Testing
A
sample
program
should
be run
to
test for
proper
interface operation.
It
is
normally
recommended
that
the “customer
complaint”
be
checked
by verifying
printer
operation
during
print-out
from
an
appropriate
program.
4

ACCESSORIES
PARTS
LIST
C 314597-01
C 314598-01
C 314598-02
C
314598-03
C 314599-01
C 1515001-01
C 903508-04
1526/802/4023
1526
MPS8O2
4023
1526/802/4023
1
526/MPS8O2
1526/802/4023
PAPER
RACK
USER’S
MANUAL
USER’S
MANUAL
USER’S
MANUAL
RIBBON
6PIN
DiN
CABLE
POWER
CORD
Cleaning
MAINTENANCE
CAUTION
L
Do
not
use
chemicals
to clean
any
of
the
printer
parts.
Using
a clean,
dry
brush,
remove
dust
and
debris
from
the
ribbon
guide,
print
head,
platen area
and
tractors
often.
Periodically
remove
the
top
case
and
brush
any
accumulated
dust
or particles
from
the
unit.
Lubrication
Oil
the
carriage
pillars,
as indicated,
every
500,000
lines
or
once
a
year.
Use
dry
guaze
to
clean
the
pillars
before
oiling.
Oil
sparingly
and
remove
any
excess,
Use
a light
oil
that
will
not
attract
and
hold
dust
and
dirt
A
clean,
light
grease
is
used
to protect
the
meshing
parts
of
the
plastic
gears.
Also,
the
4
springs
on
the
unit
may require
lubrication.
They
can
be
found
behind
the
paper
guide,
on
the
roller
unit
(2>,
and
on
the
paper
holder
(2). See
disassembly
numbers
1
2.
1
4
and
1
7
for
identification.
Be
sure
to
use
lubricants
sparingly.
CAUTION
Do
not
allow
oil
or
grease
to
contact
the
motors,
sensors, tractors,
platen,
ribbon
or
print
head.
LUB
5

Functional
Block
Diagram
Data
Flow
Theory
The
1526,
MPS
802
and
4023
printers
are functionally
the
same, with
the
exception
of
the interface
circuits.
The
1526
and MPS
802 printers have
a
serial
interface,
and
the 4023
printer
has
an
IEEE
interface.
The
data
flow
is
the same
for
all
of
the
printers.
The
Interface
The
1526
and
MPS
802
SerIal
Interface
Serial
data
is
received
at
a
rate determined
by the
clock input. The
serial
data
signal
is
inverted,
then
input
to
the IC U4D.
IC
U4D
converts
serial
data
to
parallel
data.
The
4023
IEEE
Interface
Parallel
data
(DIOl
-D108)
is received
on
the
Port B
inputs
of U4D
(PBO-PB7).
U4D
acts
as a
buffer,
allowing synchronization
between
the processor
read operation
and
the receive
data rate.
Handshake
signals
ATN
(Attention),
RFD (Ready
for
Data),
and DAC
(Data
Accepted)
provide
synchronization
be
tween the
transmitting
device
and
the
printer.
Proceseor
Logic
Printer
Data Flow
Parallel
data
from
the interface
is present
on
the
data bus
at times
selected by
the operating
system
program.
The operating
system
(program
in
ROM)
monitors
the
data
being
received
from
the inter
face. Receive
data can
be printable
characters
or
control
codes.
Printable
characters
are stored
in
RAM.
256 bytes
of RAM
are available
for character
storage.
128
bytes
of RAM
are in
U4D, and
128
bytes
in U5D.
This RAM
is called
the
TEMPORARY
LINE
BUFFER. Control
codes
are interpreted
as
special function
commands
and
are
executed
at the
time they
are received.
The number
of
lines per
inch
and the
characters
per inch
are examples
of special
function
commands.
Printable
characters
are
stored
in
the
LINE BUFFER.
When
the
carriage
return character
is received,
all the
characters
stored
in the
LINE BUFFER
are converted
to
DOT MATRIX
codes by
the
operating
system.
The
DOT MATRIX
codes are
stored
in
ROM with
the
operating
system.
The DOT
MATRIX
data is
written into
port B
of
U5D. The
driver
circuits
activate
the proper
print
wires
to
form
the
characters,
one column
at a time.
As a
character
is being
printed,
the
head
(carriage)
stepper
motor
moves one
dot column
position
at
a
time.
A
position sensor outputs
pulses
that are used
to indicate
head
position any
time it
is not home
(far
left).
The
paper
stepper motor
moves paper
up
one line
at
a
time
when
a carriage
return
is sensed.
The operating
system
program
monitors
the
position
sen
sor output,
and generates
the signals
that
are
passed to
IC U6D
port
A controlling
the motors.

—
———
——————1
I/o
A61
INDICATOR
U4D
6532
128 X 8
I
DATA
BUS
T
SERIAL
1526
INTERFACE
/
DATA
RS (RAM
SELECT)
FUNCTIONAL
BLOCK
DIAGRAM
Si
S2
(SELECT
I/O
1)
I/o
MICRO
PROCESSOR
(SELECT
I/O
2)
(SELECT I/O
3)
S3
ROM
(SELECT
ROM)
INVERTERS
PAPER
FEED
SWITCH
AO-A6
PAPER OU1
RS
HOME POSITION
DET
HEAD
POSITION
DET
DATA
BUS
DEVICE
ADDRESS
SELECTION
DATA
BUS
4023
IEEE
INTERFACE
A0
I/O
A121
AO-A6
P
0
R
T
DIO1
DIO8
DAC
RFD
ED!
ATN
B
-
RS
D
R
V
—
E
R
S
-—-,
0!
R
T 1
Si
4
6

The
Power
Supply
CIRCUIT
THEORY
The
Power
Supply generates
two
outputs,
+5VDC
and
+26VDC.
Both
outputs
are
regulated.
The
5VDC
output
supplies
the
microprocessor
and TTL
circuits,
The
+
26VDC
output
supplies
the
print
wire
coils
and
the
paper
feed
and
carriage motor
drive
circuits.
+5VDC Supply
VR1 is
a
series regulator.
The
series
regulator
keeps
the
output
voltage
constant
when
the
load
varies.
Capacitive
filtering
eliminates
most
of
the
ripple
voltage
on
the output.
CR26
is
a
full
wave
bridge
rectifier
which
converts the
AC
voltage
generated from
the
top
secondary
winding
of
the power
transformer
to DC
voltage.
+26VDC Supply
A
shunt
type
regulator
circuit
generates
the
constant
26
VDC
output.
UNREG
DC
+26
VDC REGULATOR
CIRCUIT
The
output
voltage
is
regulated
at
26,3VDC
because
the
base
to
emitter voltage
of QI
9
opposes
the
voltage developed
across
CR23.
Most
of the
load current
passes through
the
power transistor
Q23. CR27
is
a
full
wave
bridge
rectifier which
converts
the
AC
voltage
output
from
the
bottom secon
dary winding
of the
power
transformer
to
DC
voltage.
C7
filters
the
rectified
DC
output
voltage.
‘LOAD
Q23
VOUT
VF3
+ VCR23
263V
=
—7V
+27V
7

A
“low”
pulse
applied
to
the reset
interrupt
input, pin 1 of
the microprocessor
U7D,
causes the
pro
cessor
to
restart
execution
of the printer
operating system
program stored
in
the ROM U8D, A reset
pulse
occurs when the
power
is turned on. An external
device
connected
to
the
serial bus can
also
generate
a
reset,
initializing
all
devices
connected
on the bus at
the same
time.
A short
time
after the power is
turned
on, the
5VDC
supply
rises to its
normal
operating level,
This
forward
biases Q21, allowing
C3
to charge. When
the
voltage across
C3
reaches 2
volts, the
output
of
the
inverter
U1C pin 6 goes
“low”, causing
the output of
the
inverter U1C pin
4
to go
“high”.
This “low” pulse occurs
when the unit is switched
on. The reset
input — RES — on
the
serial bus
(interface
clear signal —IFC
— on
the 4023 IEEE
interface)
forces
the reset pulse
by applying
a
“low”
to
the
input of the
inverter
U1C
pin 1.
CIRCUIT
THEORY
RESET
Reset
Logic Circuit
Theory
POWER
ON
+5V
-
Q21
COLLECTOR
Ui
C5PIN
U1C6PIN
1
__________
U1C4PIN
H
APPROX.
350
ms

1526
AND
4023
CIRCUIT
THEORY
Vi
4MHz
1.15
L16
2.2H
C34
oii
flTft
+
5V
jh14zL
R56
R55
114
12
14
-
1
lii
L680
__
_
4
6C35
9
U9C
U9C
17
R57
2
LJ9C
7400
74177
n!-..
-
)___d/A 4 ,
1 MEG
HZ
11
81
LJ10C
7400
0.01
F
10
_________
7400
7400
47
)
0
Clock
Circuit
Crystal
Yl
generates
the fundamental
4 MHz
clock.
The
circuit
illustrated
below
the
crystal stabilizes
and
squares
the
signal.
U1OC
divides
the
input
frequency
by 4.
A
1
MHz
clock
is
output
on
pin
9
of
U1OC.
This
is
the
processor
system
clock.
9

CIRCUIT
THEORY
Microprocessor
Logic
Main
control
of
all
printer
operations is overseen
by
the
6504
microprocessor
(U7D).
The
6504
microprocessor
can
address
8196
locations allocated
to
RAM,
ROM,
or
I/O. The
processor
com
municates
with
two
6532
I/O
devices
(U4D
and
U5D),
a
6522
VERSATILE INTERFACE
ADAPTER
(U6D>, and an
BK byte
ROM
(U8D).
U4D
is
a
6532
I/O
device.
The
printer
interface
and
address
selection
are
controlled
by
U4D.
U5D
is also
a
6532
I/O
device.
Port
B outputs
the
signals
that
control
activation
of
the print wire
solenoids.
Port
A
signals
control the
following
functions:
1.
Paper
feed
motor
position
hold.
2. Carriage return
motor
position
hold.
3.
Paper
out
sense.
4.
Monitors carriage
position
by
counting
timing
pulses.
5.
Monitors
carriage
home position.
6. Outputs
error
LED signal.
7. Monitors
paper
advance switch.
Both
6532
I/O
devices
contain
128
bytes
of RAM.
256 bytes of storage
is
used
as a
line
buffer, and
for processor
scratch
pad
and
stack
operations.
U6D
is
a
6522
VIA.
This
device
controls
the
motors.
Port
A
signals
PAO-PA3
control
the head
motor
transistor
drivers.
Port
A
signals
PA4-PA7
control
the
paper
motor
transistor
drivers.
The pulse width
control
circuits
protect
the
print
head
by
controlling
the length
of
time current
passes
through
the
print
wire
coils.
A
555
timer
limits
this
time
to
500
microseconds.
Microprocessor
Address
Decoding
Logic
Ui D
pin
ii
goes
“low”
and
U2C
pin
12
goes
“high”
when
U4D
is
selected
by
the
processor.
Ui
D
pin
6 goes
“low”
and
U2C
pin
1
2 goes
“high”
when
U5D
is
selected
by
the processor. When
the
processor communicates
with
the
256
bytes
of
RAM
internal to the
6532
I/O
devices,
the
RS
input
on
the
selected
6532
goes
“low”
because
the
processor address output
A9
is “low”.
U1D
pin
3
goes
“low”
and U2C
pin
1 2
goes
“high”
when
the processor
selects
U6D.
U2C pin
1 2
goes “low”
when
the
processor
selects
U8D.

CC
C
cc
C
1
Q
Q
i3
01
— —
w
°
°‘
0
(Il
01
(A)
0101
01
F3W
CA)
o
>
-v-v
-v
00
0
m
mm
??
m
-
00
00
0
00
000
00
> -ø
0
0 0
-
0 0
0
%J
0
0
‘1
0

I
CIRCUITS
L___J
MICROPROCESSOR
LOGIC
I
-J
;
CLOCK
I
CIRCUIT
1
I
RESET
I
CIRCUIT
-J
PULSE
WIDTH
CONTROL
CIRCUIT
RESET
0
H
7
10

1526
AND
4023
CIRCUIT
THEORY
The
stepper
motor
holds
in
position when
the paper
is
not advancing.
This
occurs
when
a
low
value
current
passes
through
2
phases,
producing
opposing
torques
holding
the
motor in
position. Phase
A
and
phase
D are
turned
on,
and
Qi
7
is switched
off.
Current flow
is limited
by
the
470
ohm
5
watt
resistor
that
is
in parallel
with
Qi 7.
PF
Motor
0
R
w
A
N
0
M
0
T
N
STEPPING
ORDER
MO
]
Ml
M3
0
ON ON
OFF OFF
1
OFF
ON ON
OFF
2
OFF
OFF
ON
ON
3
ON
OFF
OFF
ON
4
ON
ON
OFF__[
OFF
Paper
Feed
Motor
Circuit
NOTE:
DURING
REVERSE
TRANSMISSION,
THE
CURRENT
FLOW
IS
STEPPED
IN
REVERSE
ORDER
4, 3, 2, 1,
0.
The paper
feed
motor
is
a
four
phase
stepper
motor.
Sequentially
exciting
two
phases
at
a
time
causes
the
motor
to
turn
in
step
clockwise
or
counter
clockwise. See
timing
chart
above.
Four
outputs
from
U6D,PA4-PA7,
activate
the
current
amplifier
transistors
Qi
3-Qi
6.
Current
flow
through the
emitter
collector
junction of
Qi
3,
through
phase
A
coil,
through
the
emitter
collector
junction
of
Qi 7
via
the center tap
motor
coil
excites
phase
A of
the stepper
motor.
This
occurs
when
the
PA4
output
of U6D
goes “low”,
U7B
pin
4 goes
“high”,
turning
on
Q13.
The
PAO
output
of
U5D
must
also
be
“high”,
then
U7B
pin
2 is
“low”,
and
Qi
7 is
turned
on.
CR17
CR21
suppress
CEMF
developed
by
the
stepper
motor
coils.
This
protects
the
current amps
Q13-Q16.
*WITH
NO
CR
17-21
FORCE
*WITH
CR
17 -21
COUNTER
ELECTROMOTIVE
FORCE
APPROX.
50
V
26V11____
26
100
V
ING
THROUGH
THE
COIL
11

Carriage
Motor
Drive Circuits
+26
V
CIRCUIT
THEORY
1
U6D
outputs
signals HMO-HM3
(HM
stands for
head
motor>.
Four outputs drive
the four phases of
the stepper
motor. This circuitry is similar
to the paper drive motor circuits.
Q9-Ql 2 are current
amplifiers. The phase A coil is energized when Q1
0
is turned on, Current is
passed through
the
center
tap of the motor coil, through Qi 8 to the 26VDC supply. The other
three phases are controlled the
same way. The output PAl
(CA Hold>
goes “low”, and
Qi 8
turns off
when holding
current is needed
to
hold the paper in position. Two opposing
phases are energized creating
opposing torques holding
the
motor in position. The holding currents from
the motor coils return through R5
to the 26VDC supply.
R5 limits the current flow through
the
coils, CR13 through CR16
suppress the CEMF developed by
the
coils
in the motor protecting
the
output transistors
Q9Q1 2.
U5D
6532
U6D
6522
MS
SW470fl
2 (HMO)
PAl
PAO
PAl
PA2
PA3
lkx 4 ’1t
g
34
—
U68
-I
11
10
068
068
U68
3
(HMI)
P1
ii
13 13
—
‘1
21
2222 —
cm
Q9
‘.4
CA
Motor
12

Print Wire
Drive Circuits
CIRCUIT
THEORY
U5D outputs eight signals
NDO
— ND7
(ND
= Needle
Drive>
from parallel port B
(PBO —
PB7).
These
signals are
inverted by U5B
and U6B.
The
output
of
the inverters control
current
amplifier
transistors
Qi
— Q8.
A print wire
(needle)
is
fired when
an output transistor
is forward
biased,
allowing
current
to
flow
through the coil from
the
26VDC
supply.
CR1 CR12 suppress
CEMF
developed
by
the coils.
The
inverters
U5B
and U6B are 7406
open collector
Hex/Inverters.
A
one shot
circuit generates +VCC
for U6B
and U5B
for
500
microseconds
when
a
print
wire is fired.
This
protects the print wire
coils
by
limiting
the
current
through the coils.
See Coil
Protection Circuit
and Timing
on
page
14.
13
500
iS
PuI
--TP1
1)68
24
(ND?)
56
+26
V
CR12
(24 V)’
680
Li x
8
_____
— U
CR9
L
CRBf
CR31
:-9
g;
PB?
P86
PBS
U5D
6532
P84
P83
P82
P81
P80
H:
E°
i:::E
1)68
1)58
1)58
1)58
1)58
1)58
1)58
Fl
.11
I—
11 11
Bottom
plate
88
—JWL
7?
66
55
44
—‘r
33
22
11
-
Top plate
c-
---I--
Q3
Q2
01
77iT

U6D
6522
TIMING
CHART
U6D-PBO
U
10
,s
CIRCUIT
THEORY
UBB-OUT
L
Q22COLLECTOR
I-
TP1
Print Wire
Coil Protection
Circuits
.1
500s
..1
When
a
print wire is fired,
the output
PBO on U6D goes
“low”.
This
triggers
the
555 U8B.
The output
pin
3 goes
“high”
for
500 microseconds.
This turns
on
Q20, Q21,
and Q22. The potential
developed
at the
collector
of Q20 is used
as
+ VCC for the open collector
Hex/Inverters
U58 and U6B.
R39
should
be adjusted to
obtain the
500
microsecond
pulse.
10
2
8
Vcc
Triger
reset
Reset >—
_________
6
I
CR28
TH
R39
i
20krz<
7
Cli
I
looopj
01
C9
470
p
OUT
U8B
555
+5V
+5V
t—— -,
R36
021’
3.9k
I
Q20
L — — - I
R35
Reset
circuit
1k
3
TP1
022
R37
2.2 k
R23
3.9 k
DIS
cv
GND
Lc8
ii
14

Paper
Control
Logic
CIRCUIT
THEORY
A
normally closed
micro
switch
located
behind
the
platen
opens
when paper
is
loaded
in
the
printer.
When
no
paper
is
in
the
printer,
the
switch
is
closed causing
a
“low” potential
to
be
input
at
U5D
pin
10
(PA2).
Depressing
the push button
on
the front
of
the
printer
causes
a
form
feed
to
occur.
Form
feed
length
is software
controlled.
A
“low”
potential
is
applied to
U5D
pin 1 1
(PA3)
when
the
push
button
is
depressed.
An
LED
inside the
push button
case
indicates
the
printer
is
powered
on.
A
flashing
LED
indicates
paper
out.
The
output
U5D
pin
13
goes
“low”,
U2D
pin
2
goes
“high”, and
the
LED
turns
on.
+
Ri 2
0
15K
P1
PJ
NO-PAPER SENSOR
SWITCH
+5V
PAPER ADVANCE
SWITCH
AND
INDICATOR
CIRCUIT
15