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12606B
Section III
BITS
15
14 thru 8
Table 3-2. Disc Status Word
DESCRIPTION
Sector Flag. Logic 1 indicates that the sector designated by bits 14-8 of the disc status word is not
accessible in the current disc revolution.
Next-Sector Address. Indicates address of sector which will follow the sector currently under the
read/write heads. Bit 8 is the low-order bit.
7
Disc Ready Flag. Logic 1 indicates that the disc is ready for use or is in use. Logic 0 indicates that the
disc is currently not ready for use for one of the following reasons:
a.
Low disc speed.
b.
Certain disc circuits are defective.
c.
Disc memory not connected to the computer.
d.
Disc memory not connected to the disc power supply.
e.
Low line voltage or no line voltage applied to the disc power supply.
f.
Disc power supply not turned on or defective.
6
Read Inhibit Flag. Logic 1 when the "not" Read Inhibit signal from the disc is false. Used only for
equipment troubleshooting purposes.
5
Sector Address Coincidence Flag. Logic 1 indicates that sector address coincidence has occurred since
the last STC instruction addressed the disc data channel. Logic 0 indicates that sector address coinci-
dence has not occurred. This bit is used only for equipment troubleshooting purposes.
4
Not used.
3
Abort Flag. Logic 1 indicates that bit 7 of the disc status word has been logic 0 at least once since
performance of the last STC instruction that addressed the disc data channel. Consequently, the data
transfer concerned may not have been successfully completed. Logic 0 indicates that bit 7 has been
logic 1 since the last STC instruction which addressed the disc data channel. Bit 3 is also set to logic 1 if
low AC line voltage is furnished to the disc memory power supply. Bit 3 is reset by an STC instruction
that addresses the disc data channel.
2
Writing Enabled Flag. Logic 1 indicates that the currently selected disc track is not protected by the
track protect switch. Logic 0 indicates the track is protected. This bit has significance only after a disc
track has been specified for writing by an OT A/B instruction.
1
Parity Error Flag. Logic 1 indicates read parity error has occurred. Logic 0 indicates no read parity error
has occurred. Bit 1 is reset by an STC instruction that addresses the disc data channel.
o
Disc Busy Flag. Logic 1 indicates that a disc read or write operation has been initiated, is in progress, or
is being terminated. Logic 0 indicates that none of these conditions exists. If writing or reading ends
before the end of a sector, the busy flag remains logic 1 until the end of the sector is reached.
3-29.
END-Of-TRACK.
data to or from the disc, a check of bits 3 and 1 after
completion of the data transfer provides an indication of
certain types of data transfer failure.
3-27.
READ/WRITE TRANSFER.
3-28.
At least one sector must be allowed to elapse
between the end of a read or write operation and the start
of another read or write operation. This precaution must be
observed because there is insufficient time between sectors
to program the second operation. If an attempt is made to
perform such an operation, the first operation will either be
aborted before the transfer of all data, or the second
operation will wait until rotation of the disc brings the
desired sector around for the second time.
3-30.
When the end of a gO-sector track is reached while
writing
or
reading, the operation does not continue in the
next track. Moreover, a single write or read operation must
not cross the track origin; otherwise, at the start of the new
track, writing or reading will take place starting at sector 46
(decimal) of the old track. When it is necessary to cross the
track origin, a new disc operation must be initiated after
the last sector of the track. As a result, two disc revolutions
will elapse before the writing or reading will recommence.
However, if programmed to do so, the new operation can
commence in sector 001 with the loss of only a single
sector time.
3-3
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