This information briefly explains the procedures required when issuing the EXCP and EXCPVR macro instruction. To issue the EXCP or EXCPVR macro instruction directly, perform the following tasks.

1. Allocate the data set or device to be used for the EXCP request. See Allocating the Data Set or Device.
2. Construct and open a data control block (DCB) with the DCB and OPEN macro instructions. Optionally create a data control block extension (DCBE) before issuing the OPEN macro. See Initializing a Data Control Block (OPEN)and Opening the Data Set.
3. Create a channel program containing the commands necessary to perform the I/O operations on the appropriate device. See Creating the Channel Program.
4. Create the control blocks needed to initiate the EXCP request. This includes the input/output block (IOB) and event control block (ECB), and optionally the input/output block extension (IOBE), and input/output error data block (IEDB). See Creating the EXCP-Related Control Blocks.

   For more information on specific control blocks, see Control Block Fields.

5. Issue an EXCP or EXCPVR macro instruction to pass the address of the IOB, and optionally the IOBE, to the routines that initiate and supervise I/O operations.

   After issuing EXCP or EXCPVR, issue a WAIT or EVENTS macro instruction specifying the address of the ECB, to wait for the channel program to complete. See Executing the Channel Program.

6. Once the I/O request has completed, examine the completion status of your EXCP or EXCPVR request and process any error conditions that may have occurred. See Processing the I/O Completion Status.
7. If volume switching is necessary (because of a unit exception or end of DASD extent), issue the EOV macro. See Handling End of Volume and End-Of-Data-Set Conditions.
8. When data set processing is complete, close the data set to restore the DCB. See Closing the Data Set.
9. If your program called dynamic allocation, it can optionally call dynamic unallocation.