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Status Information
After execution of a given command under either DPC
alone or under DPC and
in
cycle steal mode, status informa-
tion will be reported to the processor for analysis of that
command's execution. The three types of data that make up
this status information are:
• Condition codes
• Interrupt ID word
• Cycle Steal Status
Condition Codes
A condition code is reported to the processor for (1) every
Operate I/O instruction and (2) upon presentation of a
priority interruption. The condition code is available in
the even, carry and overflow bit positions of the Level
Status Register (LSR) in the processor. Refer to "Pre-
requisite Publications" in the Preface of this manual for
order numbers of the IBM Series/l Processor Unit
Descripton manuals. For commands that do not cause
interrupts, the condition code reported after the instruction
is executed is the only status information required or
available.
Condition codes reported at the completion of an
Operate I/O instruction are:
Condition
Code
o
1
2
3
4
5
6
7
Meaning
Device not attached
Busy
Busy after reset
Command reject
Not used
Interface data check
Not used
Satisfactory
Condition Code O-Device Not Attached
Reported by the channel when the addressed device is not
attached to the system.
Condition Code 1-Busy
Reported by the device when it is unable to execute a
command because it is in the busy state. The device enters
the busy state upon acceptance of a command that requires
an interrupt for termination. It exits the busy state when
the processor accepts the interrupt.
Condition Code 2-Busy After Reset
Reported by the display when it is unable to execute a
command because of a reset and the device has not had
sufficient time to return to the quiescent state. No
interrupt occurs to indicate termination of this condition.
3-10
GA34-0026
Condition Code 3-Command Reject
Reported by the display when:
1.
A command is issued that is outside the device command
set.
2.
The device is in an improper state to execute the
command.
3.
The IDCB contains an incorrect parameter. For
example: an odd byte DeB address, or an incorrect
function/modifier combination.
When a cycle-steal device reports command reject, it does
not fetch the DCB.
Condition Code 5-Interface Data Check
Reported by the display or the channel when a parity error
is detected on the I/O data bus during a data transfer.
Condition Code 7 -Satisfactory
Reported by the display when it aocepts the command.
These condition codes are mutually exclusive and have a
priority sequence. That is: beginning with CC=7, each
successive condition code through CC=O takes precedence
over the previous code. For example, if the display cannot
accept a command because it is busy, it reports CC= 1,
irrespective of error conditions encountered.
Condition codes reported during priority interruptions
are:
Condition
Code
Meaning
0
Not used
1
Not used
2
Exception
3
Device end
4
Attention
5
Not used
6
Not used
7
Not used
Condition Code 2-Exception
This code is reported whenever the boundary conditions
EOF, EOL or EOS are reached prior to the byte count
reaching zero, or the DCB parameters are incorrectly
specified.
This interrupt is also used when a Delayed Command
Reject, DCB Specification Check, Storage Data Check,
Device Not Ready, Invalid Storage Address, Protect Check
or Interface Data Check is detected during a cycle steal
operation. The Interrupt Status Byte (ISB) further
describes this condition.
Condition Code 3-Device End
This code is reported when no error exception or attention
conditions occur during the I/O operation. A normal
termination of the operation has occurred.
o
o
o
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