Editing Control unit (section)

== Hardwired control unit ==<!-- Front end processor redirects here -->
[[File:Animation of an LDA instruction performed by the control matrix of a simple hardwired control unit.gif|thumb|Animation of the control matrix of a simple hardwired control unit performing an LDA-instruction]]
'''Hardwired control units''' are implemented through use of [[combinational logic]] units, featuring a finite number of gates that can generate specific results based on the instructions that were used to invoke those responses. Hardwired control units are generally faster than the microprogrammed designs.<ref>{{Cite web|url=http://www.cs.binghamton.edu/~reckert/hardwire3new.html|title=MICRO-PROGRAMMED VERSUS HARDWIRED CONTROL UNITS;|website=www.cs.binghamton.edu|access-date=2017-02-17|url-status=live|archive-url=https://web.archive.org/web/20170430162916/http://www.cs.binghamton.edu/~reckert/hardwire3new.html|archive-date=2017-04-30}}</ref>

This design uses a fixed architecture&mdash;it requires changes in the wiring if the [[instruction set]] is modified or changed. It can be convenient for simple, fast computers.

A controller that uses this approach can operate at high speed; however, it has little flexibility. A complex instruction set can overwhelm a designer who uses [[ad hoc]] logic design.

The hardwired approach has become less popular as computers have evolved. Previously, control units for CPUs used ad hoc logic, and they were difficult to design.<ref>{{Cite journal |last1=Williams |first1=R. D. |last2=Klenke |first2=R. H. |last3=Aylor |first3=J. H. |date=May 2003 |title=Teaching computer design using virtual prototyping |journal=IEEE Transactions on Education |volume=46 |issue=2 |pages=296–301 |doi=10.1109/te.2002.808278 |bibcode=2003ITEdu..46..296W |issn=0018-9359 }}</ref>