The Channel Status Word (CSW) is used to provide the status of an I/O device or the status of the last I/O operation completed.  The CSW is updated when an I/O interruption occurs or as a result of an I/O command.  The CSW is available for use until the next I/O interrupt occurs or until another I/O command causes it to be replaced.

When an I/O interruption updates the CSW the I/O device causing the interruption is identified in the Old PSW as the interruption code when operating in BC mode.

The CSW has the following format:

Protection Key (Bits 0-3) indicates the protection key used for the I/O operation.

Logout Pending (L) (Bit 5) When set to one it indicates that an I/O instruction cannot be executed until a pending logout condition has been cleared.

Deferred Condition Code (CC) (Bits 6-7) Indicate a different condition code available for a Start I/O Fast Release after a condition code of zero was returned.

CCW Address (Bits 8-31) Indicate an address eight bytes greater than the last CCW used.

Status (Bits 32-47) These bits identify the condition that caused the CSW to be stored.

Count (Bits 48-63) Contain the residual count for the last CCW.

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