Outputs; Index (N Index/Sector); Index Schematic Diagram; Waveform At Test Point 7 (Soft Sectored) - Tandon TM-100-1 Operating And Service Manual

3.3.2
3.3.2.1
Outputs
Index (N INDEX/SECTOR)
Functional Description
The Index signal is provided once each revolution (200 msec, nominal) to indicate the beginning of a track to the
controller. The Index line remains in the true (low) state for the duration of the Index pulse. The duration of an In-
dex pulse is nominally 4.0 msec.
The leading edge of an Index pulse must always be used to ensure diskette interchangeability between disk
drives.
With a standard , soft-sectored diskette installed, Test Point 7 (see Figure 3-9 and Figure 3-10) is a high going
pulse, nominally 4.5 msec in duration, every 200 msec.
+5V
INDEX
TP7
EMITTER
\
1 38
J1
3
N INDEX/
2 1F
SECTOR
DRIVE
SELECT
-
INDEX DETECTOR
•
Figure 3-9
Index Schematic Diagram
___ _ , ·
n◄---------
200MSEC - - - - - - - - - - ~ - - - -
~ ~
4 MSEC AVERAGE
Figure 3-10
Waveform at Test Point 7 (Soft Sectored)
Circuit Description
The Index signal from the disk drive comes in on J4, Pin 15. The Index signal is derived from an infrared LED and
a photo-transistor detector. When the index hole in the disk drive allows the light to turn on the detector, Q8 is
turned on, sending a signal through IC 2E to IC 1 F to be gated by the Drive Select signal to produce a low output at
Pin 8 of the interface connector.
3-13