A data processing apparatus and method are provided for controlling access to a slave device, the slave device having an address range associated therewith. The apparatus comprises control storage programmable to define a partition identifying a secure region and a non-secure region in the address range, with the data processing apparatus supporting a plurality of modes of operation including a secure mode, and the control storage being programmable only by software executing in the secure mode. A master device is arranged to issue an access request onto a bus, the access request identifying a sequence of addresses within the address range and including a control signal indicating whether the access request is a secure access request or a non-secure access request. The secure region is only accessible by a secure access request. Further, access control logic is provided which is associated with the slave device, the access control logic being operable to receive the access request from the bus and an indication of the partition from the control storage and, if the access request is a non-secure access request, to prevent access to the secure region.