IBM 5256-1 Maintenance Information Manual page 159

Forms Feed Emitter
Below is a conceptual illustration of the forms feed
emitter used in the serial printer. An emitter disk
II
is
driven by the forms motor
a.
The emitter disk has 90
slots, 45 on an outer track, and 45 on an inner track.
The slots of the outer track are positioned 2 degrees in
advance of the inner track. Each slot is 4 degrees of 1
emitter disk revolution.
Two LEOs" (light emitting diodes) are positioned
opposite the 2 tracks .. Two photocells
II
face the
diodes on the opposite side of the disk. The disk turns
freely between the LEOs and the photocells so that light
from the LEOs can be sensed by the photocells. When
the disk is rotating and a slot appears in front of the
LEO, light passes through the slot, the photocell senses
the light, and current is produced. The photocells drive
2 amplifiers that convert the low level current signal
from the photocells to a TTL logic level. The signals
from the printer to the adpater are' -forms emitter A'
and ' -forms emitter B'.
~
k-4"
. - - - - . I I
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4-38
As the forms motor rotates, the forms feed emitter
produces 1 pulse for each 2 degrees of rotation. For
every 16 pulses the paper advances 1 line at 6 lines per
25.4 mm (1 inch). For every 12 pulses the paper
advances 1 line at 8 lines per 25.4 mm (1 inch). These
pulses signal the adapter that a line feed is occurring.
(The printer adapter uses these pulses to control forms
movement.)
This is a closed loop system:
'Forms emitter A' is used by the adapter to control
'forms driver A' and 'forms driver not A'.
'Forms emitter B' is used by the adapter to control
'forms driver B' and 'forms driver not 8'.
A
Adapter
.-_n_ot_A--1 The pulses are sent to the adapter to determine
the amount of motion and are used in a feed-
_---B
-I
back loop that generates forms driver pulses
not B
('A " 'not A', 'B' and 'not B' to keep the motor
operating).
I-JI~--L----.-I---------"
Forms Emitter B
I
I
~
I
I
Amplifierl-I~------_-'---L----I-r Forms Emitter A /-----'
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I
D
I
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Slot in Outer Track
D
Slot in Inner Track