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46
4.3.5
Printing Operation (See Time Chart (2), Fig. 4-9.)
The space pulse motor drives the carriage at constant speed,
and pulses corresponding to character patterns are applied to
the print head.
The carriage stays one character left of the first character,
and the space pulse motor is relatively loosely locked by the
voltage of +10 V applied to it via R24 and 02.
After completion of data input, a "1" output is sent out of
Q2's P17 output (SPACE PM OVER DRIVE) to energize transistor
TRl, which applies a +24 V to the space pulse motor to drive
the pulse motor with a powerful torque.
At the same time, pulse
signals are applied to Ql's PB4 to PB7 to drive the step motor.
The pulse motor is a 4-phase step motor.
It is arranged
internally so it has 48 magnetic "detent" steps.
Each step is
equivalent to 7.5°.
Two phases at a time are energized, the
sequence of the phases determines direction; i.e., forward is
~l,
~2
followed by
~2,
~3,
then
~3,
~4,
etc.
Two steps (15°)
are needed to advance the print head one character position
(1/10 inch).
Zener diode Z02 suppresses any CEMF voltage
generated by the motor.
When the print head reaches column one of the first character
position, printing begins.
This is accomplished by the WCPU
addressing the character generator, Q3, via output ports PIO -
P16. A LO output
=
"1".
The column is assigned by P20-P22.
P23 is data bit 8, which is the graphics bit.
Q3 outputs dot data from 00
06, pins 9-16.
pin 17 is feed
back to Q2-37 to inform the wCPU to advance the column address.
A LO output from Q3 enables the print wire.
Pin 9 is print wire
#1, etc.
This data is passed to the print head via Q6, RM3,
QIO (or Tr7 to Tr9), Qll (or TrIO to Tr13), and diode pack 012.
The outputs from Q3 are from 600 to 700
)l
s duration.
Counter voltage generated by the print head is absorbed by ZOI.
03 and 012 monitor the load of the print head.
An overload will
charge C-19 (or C-8) via Z04 and QlO-6 (or Q8-7).
This action,
via point Of" is monitored by TR3 in the power supply, and will
cut off the 24 V d.c. line if a fault occurs, thus protecting the
print head.
The pulse motor will advance and character columns will print
until the print buffer is exhausted.
Note the pulse motor will
be held in position when not advancing,
by
10
V
d.c. applied to
CN4-5 and 6 via 02 and R24.
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