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used to repeat search commands until the
desired area is lccated.
A read er write
command is then given for the desired data.
Each of the chanr.el ccmmands is acted upon
in the same manner as a control unit
ccnnected tc a Eystem/360 channel.
The
usual status is
retur~ed
after
initialization and at the completion of the
ccmnand.
sense infcrmaticn is developed
for unusual conditions and is available
through the sense ccrrmand.
A parity error
that occurs during the transfer of the CCW
causes a nachine check.
TIC Command Code
Decimal
I
Hexadecimal }
Binary
X8
l
X8
Jxxxx1000
Positions Marked "XX" Are Ignored
Figure 2-3.
Operation Code for TIC Corr-mand
2.41
SENSE
CONDITIONS, CAC
Six bytes of sense-conditions information
ar.e provided by the DAC tc
ccm~letely
identify the setting of unit-check.
These
six bytes are transferred to the system by
issuing a sense ccmmar.d (Figure 2-4).
Sense Byte 0
Sense Byte 1
Bit 0
Command Reject
Data Check in Count
Field
Bit 1
Intervention Required
Track Overrun
Bit 2
End-of-Cylinder
Bit 3
Equipment Check
Invalid Sequence
Bit 4
Data Check
No Record Found
Bit 5
Overrun
File Protected
Bit 6
Track-Condition Check
Missing Address Marker
Bit 7
Seek Check
Figure 2-4.
Sense-Byte summary CDAC)
2-24 (7/69)
2.
42
T·RACK QRIENTATION
Figure 2-5 shews the
relaticnshi~
of the
fields and zones to the track format and
Figure 2-6 shews the initializing states of
fields and zones and the command sequences
required tc perf crm a data command.
Record
Field
Zone
Field
Definition
H
Home-address area (including gaps)
C
Count area (including gaps)
K
Key area (including gaps)
D
Data area (including gaps)
Zone
Definition
Pre-record gap (including address marker)
Record
3
Cyclic code
4
Post-record gap
A
Constant gap of 12-ones bytes in the count field, or 28 all-zeros bytes
in the home-address field.
The 4.9% variable gap between records.
Notes:
The index point immediately precedes the home-address area.
*
Location of the address marker.
Figure 2-5.
Track Orientation
Sense Byte 2
Sense Byte 3
Unsafe
Ready
On Line
Unsafe
Selected Status
Cyclic-Code Check
On Line
Unselected File Status
End of Cylinder
Seek Incomplete
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