Physical Description; Printing Mechanism; Paper Handling Mechanism; Electronics - Centronics 351 Technical Manual

1.3 PHYSICAL DESCRIPTION
Physically the Model 351 is compact and
lightweight. The printer measures
approxima~ely
22 inches wide, 18 inches deep, and 8 inches high,
and weighs 47 lbs.
The printer covers include several plastic covers;
the top cover, body cover, rear cover, and base
cover. The body cover has an opening in the lower
right corner for the control panel.
There are four major assemblies within the printer:
the printing mechanism, paper handling
mechanism, electronics, and power supply.
1.3.1 PRINTING MECHANISM-The printing
mechanism consists of the print head assembly,
carriage assembly, and carriage drive com-
ponents. The carriage drive components are
~he
de drive motor, drive belts, pulleys, encoder/tim-
ing disc, and optical sensor. These components
drive the carriage and attached print head back
and forth and provide the video signals necessary
for character generation.
1.3.2-PAPER HANDLING MECHANISM-The
paper handling mechanism is capable of handling
either fanfold forms or cut sheet forms. The
mechanism consists of a stepper motor, pin feed
tractors paper guides, and drive rollers. Fanfold
'
.
forms are moved through the printer using the pm
feed tractors. Cut sheets are moved through the
printer by the paper drive rollers. The mechanism
handles up to six parts using either form.
1.3.3 ELECTRONICS-The printer electronics con-
sists of a printed circuit board (pcb) which con-
tains the format and print control logic circuits.
This Formatter/Controller pcb is located under the
printer mechanism and is attached to the printer
base. The pcb also contains the control panel
assembly and the parallel and serial input
connectors.
1.3.4 POWER SUPPLY-The fan-cooled and line-
filtered power supply is located in the left front of
the printer and is completely enclosed. The power
supply is of the switching type and is used as the
source of regulated de voltage for the printer.
1.4 PRINTER OPERATION
Basically, all printer functions can be grouped in-
3510-9800 1-3
to one of three categories:
(1)
character printing,
(2) paper motion, and (3) special functions.
1.4.1 CHARACTER PRINTING-once the data has
been received from the host device and formatted
by the Formatter/Controller circuit, the characters
are printed by selectively activating the nine print
wires aligned vertically in the print head.
As the print head moves across the paper, the ap- .
propriate print wires are momentarily activated
driving them against the ribbon, paper, and platen
to form the dot matrix pattern.
As shown in Figure 1-3, the print head is attached
to the carriage assembly, which in turn is attached
to a carriage drive belt. The carriage is driven in
the forward or reverse direction by the carriage
drive motor which rotates the belt clockwise (for-
ward direction) or counterclockwise (reverse
direction).
1.4.2 PAPER MOTION-Paper is moved by press-
ing one of the paper motion switches: line feed
(LF), paper forward (PAPER FWD), paper reverse
(PAPER REV) or form feed (FORM FEED) located
on the pcb, or by receiving a paper motion com-
mand from the host device.
Physically, paper is moved by the torque from t~e
paper stepper motor which is applied to the pm
feed tractor drive gears and the rollers which move
the paper up or down as shown in Figure 1-3.
1.4.3 SPECIAL FUNCTIONS-As a standard
feature, the printer is capable of printing in a
unidirectional graphics mode or bidirectional
graphics mode. The graphics mode is selected by
an escape sequence control code and the
graphics program is completely controlled by the
host device.
Also as a standard feature, the printer has a self-
test capability which is activated by placing a Dip
switch (S2-4) on and depressing the SELECT
switch. Printing of test data will be repeated each
time the SELECT switch is depressed.
In addition to the printable character codes, the
printer also recognizes certain special control
codes and escape sequences. Refer to the users
manual for a list of the codes and the printer ac-
tion performed on receiving these codes.