Status Word - Adaptec AHA-1740A Technical Reference Manual

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Status Word

The status word is a 16-bit structured field used to hold flags indicating how the com-
mand for the associated control block is completed.
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Fields that are empty are reserved and will be set to zero.
Flag Name and Function
DON Command Done - No Error
The Command Done flag (bit 0) indicates whether the control block completed suc-
cessfully.
If this bit is one, the control block completed without error.
If this bit is zero, the other flags in this word as well as the host adapter and target
status bytes should be analyzed to determine the completion status of the control
block.
When this flag is zero, the status block is stored unconditionally by the host adapter
and an interrupt is generated, regardless of the settings of the Disable Interrupt
and Disable Status Block flags (Flag Word 1, bits 7 and 14, respectively).
DU Data Underrun
The Data Underrun flag (bit 1) indicates whether the amount of data transferred
was less than the amount specified by the data length field in the control block.
If this bit is one, a data underrun occurred. the residual byte count and residual
buffer address fields are valid. If the Suppress Error on Underrun flag (Flag Word
1, bit 10) was set to one, then the Command Done flag will also be set to one,
indicating that the underrun condition was not considered an error. If the Suppress
Error on Underrun flag was set to zero, then the Command Done flag will be set to
zero and the Major Error/Exception flag will be set to one.
If this bit is zero, no underrun condition was detected.
QF Host Adapter Queue Full
The Queue Full flag (bit 3) indicates that the host adapter was not able to accept
the control block.
If this bit is set to one, the host adapter has rejected the control block because its
internal storage area is full. No action is taken on the control block. The host should
reissue the control block after an outstanding control block completes or after an
appropriate time delay.
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AHA-1740A/1742A/1744
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