2732 Eprom; Power Supply L_G; Print Head 1_8 - Atari 1025 Field Service Manual

3051
MICROPROCESSOR
The
microprocessor
controls the overall functioning of the
printer.
It
reads the
information the
computer wants
printed through the I/O
cable, looks up the proper
character
in
the
ROM
chip and by
controlling
a
series of High and
Low
signals prints
the character on the
paper.
The
microprocessor operates
off a 7.37
MHz
clock,
which
acts as the
known
frequency
whereby
all
functions of the
MPU
are
timed
to interact.
8155
RAM
I/O
This chip has
two
functions:
1) It
provides the
Random
Access
Memory
storage
for
the
printer, that
is, it
stores information
that
is
subject
to
change
(for
example, which character
set
is
currently being
used).
2)
The
8155
also controls the driver
lines that operate
the
line
feed and space
motors.
2732
EPROM
This chip contains the information that
determines how
the characters are
formed
in
all
of the different type
faces.
POWER
SUPPLY
The 110V A/C
is
fed
into
a transformer by the
power
cord.
26VAC
and
10VAC
are
output.
The 26V
AC
runs through
a bridge
rectifier
and
supplies voltage
to the
motors
and
print head.
The
10VAC
runs through
a rectifier and
supplies
10VDC
to
the printer
and
a
5V
regulator.
This regulator delivers the voltage
to
the
logic circuitry
of the
PRINT
HEAD
The
following discussion describes
what
occurs
electronically
in
order
to print the
Letter
I.
The computer
console
signals the 1025
to get ready
to print a
letter
by
pulling the
command
line (pin 7
of
CN6
or
CN7)
Low.
This
in
turn
pulls
down
pin 14 of
Q8.
The computer
then sends the information
to the microprocessor
via the
Data
In
line.
If
the
printer did not
for
any
reason
accept
the information sent by the
computer,
it
sends a code back
to the computer
telling
it
what
caused
the
failure.
If
the processor accepts the computer's information,
it
temporarily
stores
it in
the 8155.
It
then
looks up
what
the
print
head
pattern should be
for that character,
as
determined
by
the information
permanently
stored
in
the
ROM,
and
gets ready
to print
Atari 1025 Printer
Field Service Manual
1-8