Abstract: A data processing system (10) capable of burst transfers having an external bus interface (30) which allows termination of a burst transfer prior to completion of the burst transaction. The present invention offers a method of terminating a burst transaction without the addition of wait states, and further allows termination to effectively interrupt the burst transaction rather than waiting for burst completion. In one embodiment, on the negation of a burst request signal during a burst transfer, external bus interface (30) terminates the burst transfer without waiting for the completion of the burst transaction.

Abstract: A data processing system (20) having a burst address generator (BAG) 55, with a programmable transaction mode applicable to both cache and pre-fetch architecture types. BAG 55 asserts a data acknowledge (DTACK) signal to end a burst transfer on either a physical boundary, as in pre-fetch mode at the end of a row in a memory device, or a limit detection, as in cache mode where the limit is determined by the length of a cache line. BAG 55 increments the burst address internally, and for operations in pre-fetch mode, the user determines if the incremented address is provided external to data processor (22).

Abstract: A data processing system (20) having a high performance chip select (HPCE) signal, which is functionally programmable to remain asserted for a predetermined number of bus cycles based on an access duty cycle. Bits in an option register (52) allow the user to program HPCE for maintained assertion always, never, or for a number of cycles after a last valid address match. Continued assertion reduces access time to an external device allowing the user to determine the trade-off between high speed access and low power consumption. Additionally, a speculative burst access is made without regard to match criteria, allowing a device to prepare for access while data processor (22) determines the next device to access. Here a load burst address (LBA) signal is speculatively provided to an activated device, and where the next access is to another device, the speculative access is aborted.

Abstract: A data processing system (10) allows an authorized user to unlock a security mode by providing a code stored in a plurality of mask registers (60,62,66) such that the system is selectively allowed to communicate with an external device. When an reset signal is received, a selector (48) selects a first mask register (60) and retrieves a first stored address value and a first stored data value therefrom. The first stored address and data values are respectively compared with a first address value and a first data value by a comparator (44). This process of selecting and comparing continues until a final match signal is asserted. When the final match signal is asserted, a secure signal is negated and the system may communicate with the external user.

Abstract: Data processor (10) configures internal circuitry during execution of a reset operation in response a logic state of a Mode Select signal. If an external bus control (44) determines the Mode Select signal is in a first logic state, configuration data is provided from a mask register (40). The data is transferred to a plurality of configuration registers (50) and, subsequently, to a remaining portion of data processor (10). If the Mode Select signal is in a second logic state, configuration data is provided from a plurality of bus terminals (48). The data is transferred to the plurality of configuration registers (50). The contents of the plurality of configuration registers (50) are transferred to bus interface unit (42) which subsequently transfers the data to a remaining portion of data processor (10).

Abstract: A mask programmable register (40) determines a default configuration of a data processor during a reset operation. The default configuration is driven to a plurality of external integrated circuit pins (48) of the data processor with weak drivers (528, 534, 540, 546). Then, on an individual pin basis, an external user (11) may choose to allow each integrated circuit pin to remain in a default state or be drive with an external configuration value. When the external user chooses to allow the integrated circuit pin to remain in the default state, an internal default configuration data value provided by the internal mask programmable register is output by the integrated circuit pin. Conversely, when the external user chooses to override the default state, the user may drive the external configuration value to the integrated circuit pin using an external data source.

Abstract: Method and apparatus for performing read accesses from a counter (40) while avoiding the large rollover error that may occur when the counter (40) is read using more than one read access cycle. In one embodiment, the present invention monitors the most significant bit of the lower portion (44) of counter (40) for a transition indicating that a rollover has taken place. If a rollover has not occurred, read accesses take place in the normal manner. However, if a rollover has occurred during the latency period between a read access from the upper portion (42) of counter (40) and a corresponding read access from the lower portion (44) of counter (40), the read access from the lower portion (44) is inhibited and a default value is placed on the bus (36) instead.