This appendix describes the normal sequence of I/O channel control words (CCWs) within channel programs for the communication controller and channel-attached devices. If you determine that the problem is in an I/O sequence, you need to know the normal sequence of I/O CCWs within these channel programs. With a dump, the VIT trace with the CIO option, or a CCWTRACE (if available), you can compare the sequence that happened with the expected sequence. When there is a deviation, you can then look at status and sense bytes returned from the communication controller or the cluster controller for information that can help you determine the location of the error condition.