Department of Computer Science and Technology

Technical reports

The SKIM microprogrammer’s guide

W. Stoye

October 1983, 33 pages

DOI: 10.48456/tr-40


This paper describes the design and implementation of the SKIM micorprocessor. The processor has a 24 bit ALU with 16 general purpose registers. The main unique feature is a large microcode store of up to 64K 40 bit words, with the intention that the microcode could be used like the machine code on a conventional processor, with operating system primitives being programmed in microcode.

The processor has been constructed from TTL logic, with a microcode assembler running on Phoenix. A debugger for both the hardware and microcode programs runs on the host machine, currently a BBC Microcomputer.

The processor architecture is discussed, with examples of microcode programming. comparisons with other processors are made, and some of the limitations of the present design are noted.

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BibTeX record

  author =	 {Stoye, W.},
  title = 	 {{The SKIM microprogrammer's guide}},
  year = 	 1983,
  month = 	 oct,
  url = 	 {},
  institution =  {University of Cambridge, Computer Laboratory},
  doi = 	 {10.48456/tr-40},
  number = 	 {UCAM-CL-TR-40}