Department of Computer Science and Technology

Technical reports

The SKIM microprogrammer’s guide

W. Stoye

October 1983, 33 pages


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},
  number = 	 {UCAM-CL-TR-40}