Radio Shack TRS-80 Service Manual page 110

termination of the WRITE ENABLE signal. When the
WRITE ENABLE line is false (high), aU write electronics
are disabled.
When a write protected diskette is installed in a Disk Drive,
the write electronics are disabled irrespective of the state of
theWRITE ENABLE line.
sIDe SELECT (SDSELI
When this signal is true (low), one side of
iI
double-headed
drive is selected. When this signal is false (high). the other
side of the drive
i$
selected.
OUTPUT STATUS
(See Table 1)
INDEX PULSE lip·)
The INDEX PU LSE signal is prOIlK.led once each rellOlution
(200 mSec. nominJll) to indicate to the controller the begin·
ning of a track. The INDEX PULSE line remains
in
the true
(low) stilte for the duration of the INDEX PULSE IThe
duration of an INDEX PULSE is nominally 4.0 mSec).
The leading edge of an INDEX PULSE must always be used
to ensure diskette interchangeability between Disk Drives.
TRACK
110
ITRKO·)
When the Disk Drive is selected, the TRACK 60 interface
signal indicates 10 the conlroller that the read/write head is
positioned at Track 00. The Tr<K:k 00 remains true (low)
until the head is moved away from Trilck
013.
WRITE PROTECT (WPRP)
When the Disk Drive is selected, this signal line logic level
goes lrue flow) \Nhen the diskeHe is write protected. The
write etectronics are internally disabled when the diskette
is write prolect@(.!.
NOTE; It is recommended that the wrile data line be in·
active whenl:!\ler Write Enable is false li.e., read sUle).
When the level on lhis line is false (highl, the write electron·
ics are enabled and the write operation can
be
performed. It
is recommended that the controller not issue a write com·
mand when the WRITE PROTECT signal is true (lowl.
READ DATA IRO·)
This interlace line trJlnsmiu the readbaek dau to the con·
troller when the Drive is selected. It provides a pulse for
each ftux transition recorded on the medium. The READ
DATA output line goes true (low) for a duration of l.uSee
for each flux c:hange recorded.
The leading
edge
01 the READ DATA output pulse repre·
sents the true positions for the flux transitions on the disk-
ette surface.
103