Editing IBM PCjr (section)

===Sound===
[[File:IBM PCB Jr Internal.jpg|thumb|IBM PCjr internals|alt=]]The PCjr's sound is provided by a [[Texas Instruments]] [[SN76496]] which can produce three square waves of varying amplitude and frequency along with a noise channel powered by a [[shift register]].<ref name="nortonpcjraudio19840124">{{cite news | url=https://books.google.com/books?id=kSzKzjWHeVEC&pg=PA137 | title=Sound Abilities: The PCjr | work=PC Magazine | date=January 24, 1984 | access-date=October 23, 2013 | author=Norton, Peter | pages=137}}</ref> It is similar to the [[programmable sound generator]] chips used in game consoles such as the [[Master System]]. The PCjr design also allows for an analog sound source in an expansion-bus "sidecar" module, and a software-controlled internal analog switch can select the source for the sound output from among the [[PC speaker]], the SN76489, the cassette port, or the expansion-bus sound source. Only one sound source can be selected at a time; the sources cannot be mixed.