Abstract: A data processing system (100, 300) allows an individually mappable word of memory to patch a desired memory location. During operation, a memory system (130) monitors an address/control bus to determine when an access to a specified word in a system memory (120) occurs. When an access to the specified word occurs, address comparators (140) determine if a memory location to be patched is being accessed, and provides an active signal to the access control circuit (150), which prevents data flow with the system memory (120) and enables the data flow with a separate memory (170) by controlling a transmission gate 115. Therefore, the data access occurs from the separate memory and not the system memory.

Abstract: A data processor with development support features includes an alternate mode of operation in which instructions are received by means of an externally-controlled path. The connections used by the externally-controlled path are not shared by any system resources accessible to the data processor in the normal mode of operation, but are used by other development support features in the normal mode. In a preferred embodiment, an integrated circuit microcomputer includes such a data processor as its CPU. The CPU has access to on-chip peripherals and memory, in addition to off-chip peripherals and memory, in both the normal and alternate modes of operation, by means of a parallel bus which it operates as a bus master. In the alternate mode, the CPU receives instructions by means of a serial bus on which the CPU is a slave device.

Abstract: A data processing system having a debug peripheral is provided. The debug peripheral is coupled to a central processing unit and memory via an internal communications bus. The debug peripheral is a single-word dual port memory with parallel read-write write access on one side, and synchronous, full-duplex serial read-write access on the other side. The serial side of the debug peripheral is connected to external emulation hardware by means of a three-pin synchronous serial interface. The parallel access is via a connection to a core central processing unit (CPU) internal communications bus. The debug peripheral is addressed at sixteen adjacent locations in the CPU memory space. During a debug interlude, the debug peripheral assumes control of the CPU by providing an interrup signal to the CPU, and thereby causing the CPU to fetch instructions directly from the debug peripheral.