Section Ill. TECHNICAL PRINCIPLES OF OPERATION
1-16. FUNCTIONAL DESCRIPTION
T h e line printer functions as an output terminal which produces hard copy printout
for use with an automated data processing system. When on line under control of a
s y s t e m Central Processing Unit (CPU), the line printer serves as a parallel-input
t e r m i n a l capable of receiving 8 bits at a time. Maximum print rate on line is 132
characters at 1060 lines per minute at a print density of 6 or 8 lines per inch.
Functions, once implemented under hardware control by the operator, are under
Interface with the system CPU is
c o n t r o l of the printer processor circuit board.
a c c o m p l i s h e d by the interface circuit board. T h e processor circuit board functions
as the computing center of the printer system. I t controls and stores the
printable data, performs the comparison between user-generated character codes for
c h a r a c t e r s on the print line and character codes for characters on the print band.
The processor also decodes control characters into system commands and stores
Vertical Format Unit (VFU) data. T h e r e is also a timing and status circuit board
w h i c h interfaces with the processor circuit board to monitor printer operation such
as control and synchronization of the character band and firing of the hammers.
The timing and status board also contains circuitry which detects power supply and
o p e r a t i o n a l fault such as printer hot condition, band speed faults, band drive
o v e r c u r r e n t conditions. Operational condition and fault codes are displayed on the
c o n t r o l panel status indicator. These digital codes (table 3-1) are used during
o p e r a t i o n and troubleshooting.
1-17. SELF-TEST MODE
A self-test mode is provided as an operator aid to check printer operation and to
a l l o w printer troubleshooting without the need of an external system exerciser
program. Self test may be selected by placing the TEST switch on the control panel
t o either the left or right operating position, then placing the printer on line by
pressing the ON/OFF LINE switch. After the printer has been placed on line by
p r e s s i n g the ON/OFF LINE switch, the processor circuit board will then inhibit the
i n t e r f a c e data load mode, allowing the data buffer to be loaded from printer
internal sources rather than from the user system. With the TEST switch in the
right hand position, pressing the ON/OFF LINE switch will cause the printing of a
s l i d i n g p a t t e r n . P l a c i n g the switch in the left hand position will cause the
p r i n t i n g of a fixed character pattern. A f t e r printing in either the sliding or
f i x e d position, the switch may be moved to the center position. The printer will
r e m a i n in the self-test mode, printing the same pattern previously printed at
o n e - h a l f full printer speed. S h o u l d a fault or interlock condition be detected,
t h e processor circuit board will take the printer off line and direct an
appropriate fault code to be displayed on the control panel STATUS indicator. A
s t a t u s code of 66 or 67 indicates that the printer is in the self-test mode. The
self test is terminated when the ON/OFF LINE switch on the control panel is
pressed, and the TEST switch is then placed in the OFF position.
1-18. PRINTER MECHANISM
The printer mechanism which is housed in the upper level of the acoustic cabinet
forward of the logic cards consists of a character band drive system, a ribbon
drive system, the form movement mechanism, a printer subsystem, and a power