| 摘要 |
A microcode patch apparatus including a patch array, a mux, and a RAM. The patch array receives a microcode ROM address and determines that the microcode ROM address matches one of a plurality of entries within the patch array. The patch array outputs a corresponding branch instruction and asserts a hit signal. The branch instruction prescribes a microcode branch target address. The mux receives the branch instruction from the patch array and a micro instruction corresponding to the microcode ROM address from a microcode ROM. The mux provides the micro instruction or the corresponding branch instruction to an instruction register based upon the state of the hit signal. The RAM stores a plurality of patch instructions that are to be executed in place of the micro instruction. The first one of the plurality of patch instructions is stored at a location in the RAM corresponding to the microcode branch target address.
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