Patent ID: 7406406

Claim:
In a data processing system in which a structure and operation of a target system, which includes accumulator and supplementary accumulator registers, is emulated on a host system and in which a word length of the target system is shorter than, but more than half, a word length of the host system, a process for providing, during an emulation process, visibility in the emulated accumulator and supplementary accumulator registers of a target system word stored in the host system memory, the process comprising the steps of: A) in response to a first target system instruction to be executed during the emulation of a target system program by the host system, which first instruction includes an opcode specifying a first now functionality for reading entire content of an identified full word from the host system memory, and for providing the entire content of the identified full word to the target system program by: 1) identifying a first storage location in the host memory system, and 2) loading the lower order contents of the first storage location into the emulated supplementary accumulator register; and 3) loading the remaining contents of the first storage location into the least significant bits of the emulated accumulator register; and B) in response to a second target system instruction to be executed during the emulation of a target system program by the host system, which second instruction includes an opcode specifying a second new functionality provided to the target system program for writing into an identified full word of the host system memory by: 1) identifying a second storage location in the host memory system, and 2) storing the contents of the emulated supplementary accumulator register into the least significant bits of the identified second storage location; and 3) storing the least significant bits the accumulator register into the most significant bits of the identified second storage location so as to fill all bits of the full word in host system memory at the identified second storage location.