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Sense Release
This command releases the reserved tape control. A Sense. Release command is
honored only when issued by the channel which had reserved that tape control.
The Sense Release command should only be issued by the Control Program.
Programming Note; Sense Reserve and Sense Release commands can only be
used on subsystems having the two-channel switch feature.
If
these commands
are issued to a tape control without this feature, Command Reject results. When
using these commands, they must be the first command in a chain or Command
Reject will result.
The Sense Reserve and Sense Release commands are not supported by IBM's
Operating Systems.
Request Track-In-Error (Request TIE)
Request
TIE
returns to the tape control a data byte containing track-in-error
information for nine-track tape units and sensing level information for
seven-track tape units. This information was transmitted to the channel in Sense
Byte 2 following a Read, Read Backward, Write, or Loop-Write-To-Read
command.
When issued following a 6250 or
PE
operation, Request
TIE
is treated as No-op
Reset Sense.
When issued following a nine-track
NRZI
read operation, a Request
TIE
conditions the tape control for a corrective read.
When issued following a seven-track read operation, the request
TIE
byte
controls the read clipping level. See Sense Byte 2 for details.
Loop Write-To-Read (LWR)
Set Diagnose
This is a write command that checks the tape control and tape unit data and
control paths but does not move tape. In 6250 or 1600
BPI
mode,
L WR
writes
and error checks the record. In
NRZI
mode,
L
WR
writes the record but error
checks only Write Trigger
YRC
and the Channel Buffer Check.
On nine-track 3420 tape units, a
LWR
command issued at
BOT
is executed in
1600
BPI
mode. Elsewhere on tape,
L WR
is executed in the current operating
mode of the tape unit.
L
WR
does not require the tape unit to be in write status, but the tape unit must
be 'ready.' Execution of an
LWR
does not change the status of the tape unit. A
LWR
performed from the
CPU
uses the same data path as a Write command.
This command is used to summon microdiagnostic routines. Four bytes are
transferred from channel to the tape control to modify the operation of
succeeding commands in the chain.
,
Motion Control Commands
Motion control commands move tape but do not transfer data across the
channel/ tape control interface.
All motion control commands operate as follows:
1. Channel End is signaled when the command is accepted (initial status).
2. Device End is signaled when the operation, except for Rewind Unload (see
below), is completed (ending status).
24
3803-2/3420 Subsystem Description
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