7-8. Led/Ptx - IBM 6360 Product Support Manual

LEO/PTX
A Light Emitting Diode (LED) and a
Phototransistor (PTX) are used to
sense diskette rotation (Figure 7-8).
The diskette has a small hole in its
inner edge which passes the LED and is
sensed by the PTX with each
revolution. As the diskette continues
to turn, the light to the PTX is cut
off. This causes a light pulse six
times per second or every 166.7 milli-
seconds. These pulses indicate to the
file control card that the diskette is
PTX
turning and are reference points for
the diskette· adapter to check the
speed of the diskette (360 Revolutions
per Minute (RPM). Operation of the
diskette drive will continue normally
if the pulse period· does not change
from 166. 7 ms by more than 4.2 ms
(162.5 ms to 170.9 ms).
The type 2D drive operates the same
except the LED is a dual LED that also
indicates to the file control card the
type of diskette turning in the drive.
I ndex Hole (Type 2D Drive)
Figure 7-8. LED/PTX
Chapter 7. Diskette Unit 7-9