Track Crossing Sensor/Fine Home Sensor; Carriage Photocell; Carriage Photocell Signals - IBM 5444 Manual

Drive Disk
Leadscrew
Fine Home
Lamp
Figure 1-34. Track Crossing Sensor/Fine Home Sensor [ 07494]
output is fed to a photo-amplifier to provide the
'carriage pc lit' line which is used to produce three other
lines: 'coarse home', 'add write current', and 'all cells lit'
(Figure 1-37).
'All cells lit' is used in the machine start-up sequence
to retract the heads from track 010 to track 000, prior
to head loading.
'Add write current' is held on by the 'add write
current' latch, which is set by 'carriage pc lit' during the
machine start-up sequence. 'Carriage pc lit' drops when
the coarse home flag passes the photocell (between
tracks -020 and +005) and raises the 'coarse home' line.
When t~e heads leave track 000, the coarse home flag
moves away from the photocell, activating 'carriage pc
lit' at track 005 to drop 'coarse home' and raise 'add
write current'. At approximately track 115, the add
write current flag passes the photocell and drops
'carriage pc lit'. The 'add write current' latch resets at
track 120 when the next 'fine home area' pulse occurs.
The 'add write current' latch is not set again until the
heads are retracted below track 115, reactivating
'carriage pc lit'.
Track 000 (Home) Indication
• Track 000 is indicated by the logical combination of
the "track crossing', 'fine home area', and 'coarse
home' signals.
1-18 (5/70)
Hole in Sensor Mask
Fine Home Sensor Arm
(sectioned to show
Sensor Mask
Fine Home
Sensor Arm
Mounting
sensor mask and drive disk)
Fine Home Hole
Track Crossing
Slots
Figure 1-35. Drive Disk and Sensor Mask [07495]
Add Write
Current Flag
Photocell
Figure 1-36. Carriage Photocell [07496]
File Track Crossin
Carriage PC Lit
Fine Home Area
Home Area Latch
Forward Direction
Coarse Home Flag
5 us
Figure 1-37. Carriage Photocell Signals [07497]
Add Write
Current
FL
FN470
All Cells Lit
Add Write Current
Coarse Home