Tandy 1000 HX Technical Reference Manual page 378

3.3.6 WRITE GATE
When this line is made true (low) while a drive is selected,
the write current circuits are enabled and information may be
written under control of the WRITE DATA input.
3.3.7 WRITE DATA
If the WRITE GATE is true (low) , a true pulse (low) on the
WRITE DATA line causes a bit to be written on the disk.
Pulses on this line are neglected when WRITE GATE signal is
false (high).
No pre-compensation is required.
3.3.8 INDEX
When the drive is selected, a true (low) pulse is generated
on this line by each revolution of the spindle.
3.3.9 TRACK 00
This line is true (low) when the drive is selected and the
Read/Write head is positioned on track 00.
3.3.10 WRITE PROTECT
If a write-protect disk is inserted while a drive is
selected, this line will be true (low) and the drive will not
be able to write data. At all other times, except when a
disk is ejected while the drive is selected, this line will
be false (high).
3.3.11 READ DATA
When the drive is selected, a true (low) pulse is generated
on this line every time a bit is detected.
3.3.12 DISK CHANGE
This line is true (low) whenever a disk is removed from the
drive. The line remains true (low) until both the
following conditions have been met:
1. A disk is inserted,
and
2. A STEP pulse has been received when the drive is selected.
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