Service manual
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 (0101-DI08) is received on
the
Port B
inputs
of
U4D
(PBO-PB7).
U40
acts
as
a
buffer,
allowing
synchronization
between
the
processor
read
operation
and
the
receive data rate. Handshake
signals
ATN
(Attention),
RFD
(Ready
for
Oata), and DAC (Data
Accepted)
provide
synchronization
be-
tween
the
transmitting
device and
the
printer.
Processor
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
U40,
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
OOT
MATRIX
codes are
stored
in ROM
with
the
operating
system.
The DOT
MATRIX
data
is
written
into
port
B
of
U50.
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
U60
port
A
controlling
the
motors.
0101
1
0108
DAC
RFD
EDI
ATN
SERIAL
1526
INTERFACE
I
----I
I
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I
110
DATA
,~I
nr.K
~TN
t----I
PORT
A
INVERTERS
U4D
6532
DEVICE
ADDRESS
SELECTION
4023
IEEE
NTERFACE
----
128
X 8
1-----
r---~
PORT
1
-
B
I/O
--------------1
P
_______________
-1
0
----------------1 R
-----------------i T
---------------4
B
U4D
6532
RS
---
128
X 8
0
---
R
--,
I
P
I
V
0
1
E
R
R
I
S
T
I
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I
A
f
I
- I
AD - A61
- I
RS
S1
AD -
A6
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J
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DATA
BUS
S1
I
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6504
MICRO-
PROCESSOR
U7D
DATA
BUS
FUNCTIONAL
BLOCK
DIAGRAM
f---
RS
(RAM SelECT)
110
ADDRESS
BUS
ADDRESS
r--
-S1
(SELECT
110
1) I P
t::
DECODE
r--
S2 (SelECT
110
2) I 0
PAPER
FEED
SWITCH
LOGIC
r-- S3 (SelECT I/O 3)
II
~
t---.......--....I~UT
~F
PAPER
INDICATOR
ROM
(SELECT
ROM)
PAPER
OUT
r-- AD _
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DET
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6532
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HEAD
POSITION
DET
U8D
ROM
8K X 8
DATA
BUS
AD -
RS
---
--
OPERATING
t-------------I
SYSTEM
S3
___
L
128
X 8
1-----
PORT
B
I/O
r
-t----I
DRIVERS
PRINT
WIRES
(NEEDLES)
t---I
DRIVERS
HEAD
MOTOR
PRINT
HEAD
I
I
1----
.......
-
---
-
I P
1--_-1
1
0
PAPER
MOTOR
U6D
I R
65221T
HEAD
POSTION
DETECTOR
I A
.....
-----------'
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