To obtain the performance improvement given by rotational position sensing, specify the sector_addr parameter in the XDAP macro. For programs that can be used with both RPS and non-RPS devices, test the UCBRPS bit to determine whether the device has rotational position sensing. If the UCBRPS bit is off, do not issue a channel program with a set sector command to the device.

The sector_addr parameter on the XDAP macro specifies the address of a 1-byte field in virtual storage. Store the sector number of the block to be located in this field. You can obtain the sector number of the block by using a resident system conversion routine. See Obtaining the Sector Number of a Block on an RPS Device