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The IBM 5256 Printer is powered by two stepper
motors: the carrier motor and the forms motor. Each
motor is controlled by 4 drive lines: 'A', 'not A', 'B', and
'not B'. Combinations of these drive lines in a
prescribed sequence determine the direction the motor
turns.
The carrier motor is coupled to a carrier that supports
the ribbon box, the ribbon drive mechanism, the print
head, and the print emitter pickup.
The ribbon box holds a continuous loop of ribbon. The
ribbon is driven by 2 lines through 2 clutches and a
series of idler gears.
The print head contains 8 vertically-mounted print wires.
Signals from the printer adapter move the print head
along the print line and selectively energize the print
wires.
The character dot matrix is 8-high and 7-wide. The 8th
wire is used for underscoring, for some special
characters, and for some lowercase letters.
The print emitter pickup consists of 4 land patterns and
4 associated amplifier detector trigger circuits. Three of
the land patterns are vertical; the 4th is horizontal (all
reference to land pattern direction in this overview are
with the printer in the service position). The print
emitter pickup slides along the length of the print
emitter board.
The print emitter board is a stationary board with 1
continuous vertical land pattern and a 4.25 MHz
oscillator.
A print emitter pulse is produced when the land pattern
of the print emitter board and one of the vertical land
patterns of the print emitter pickup are at a maximum
misalignment (null position). The maximum misalignment
of a vertical print emitter pickup land pattern and the
vertical part of the print emitter board land pattern
occurs every 0.76 mm (0.030 inch). Because each
vertical print emitter pickup land pattern is displaced by
0.25 mm (0.010 inch), a print emitter pulse occurs every
0.25 mm (0.010 inch).
When the horizontal land pattern of the print emitter
pickup is aligned with the horizonal part of the print
emitter board land pattern, a left margin pulse occurs.
The print emitter pulses and the left margin pulses
energize 4 lines:
Emitter 1
Emitter 2
Emitter 3
Left margin
When these lines are active, they signal the adapter:
• When the print head is in the left margin area (during
initialization only).
• Where the print head is during printing.
Which direction the print head is moving.
• When to fire the print wires.
The printer adapter is contained on a half planar located
within the printer. This planar contains:
a cable adapter
control storage (R05-read only storage)
data
stor~ge
(read/write storage)
a microprocessing unit (MPU)
printer input registers and a character generator
emitter control
forms control
sense latches
controls for the operator switches and lights
counters, decodes, and register selection circuits.
The cable adapter receives commands -and data from
the host system over the cable. The adapter responds
to the poll commands and read activate commands
through hard-wired address decodes. For write activate
commands, the MPU assigns buffer space and provides
the beginning and ending addresses in an address
buffer. The cable adapter uses these addresses to
locate space in data storage for data that follows the
activate command.
Theory.
Features
Theory
5256 MIM
4-3
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