Editing Jumper

In computer keyboard terminology, a '''jumper''' or '''jumper wire''' refers to a wire soldered between two points on a [[printed circuit board]] (PCB) to assist with trace routing. The term "jumper" is used by Cherry in the specifications of the [[Cherry MX]] keyswitch despite the alternative use of "jumper" to refer to a configuration shunt.<ref name="Cherry-MX-spec" />

In keyboards without [[diode]]s, routing all the matrix wires in accordance with [[Rollover, blocking and ghosting|2-key rollover]] is difficult. Jumper wires allow traces to "tunnel" under the PCB so that they effectively cross over other traces.

There are several approaches taken to routing traces:

;Multi-pin switches
:Switches such as [[Omron B3G-S series]] and the [[KPT switch]] have three pins, with two of them being connected by one of the contact plates; additional traces can then be run underneath the switch, with the switch functioning as a jumper wire.<ref name="KPT-102" /> There are also various switches with four pins.
;Integrated jumpers
:The [[Cherry MX]] series has two holes at the front of the switch, which can accommodate a jumper, a diode, or an [[LED]]; [[Alps SKFR/SKFS series]] switches also feature integrated jumpers. [[Alps SKFL series]] and [[Mitsumi miniature mechanical]] are both examples of switch designs where part of the switch itself (the metal lid) is conductive and forms a jumper.
;External jumpers
:The PCB can simply have pieces of wire soldered between traces outside of any switches. On keyboards with [[N-key rollover]], the [[diode]]s also provide this purpose, as seen in the PCBs for the [[NEC PC-8201A]] and [[Zenith Supersport SX]].

<gallery widths=250 heights=187>
File:Alps SKFSAA -- tactile leaf in-place.jpg                | Brass-coloured jumper at the back of an Alps SKFSAA switch (top of picture)
File:Cherry MX Clear -- opened, with jumper wire visible.jpg | Jumper wire inside a [[Cherry MX]] switch (bottom of picture)
File:Cherry MX-M8 Adapter -- jumper removed.jpg              | Jumper wire removed from a Cherry MX switch
File:Sasse SPST-A2 -- jumper partially removed.jpg           | [[Sasse SPST]] "A2" with jumper partially removed; the jumper shape allows it to fit in the diode bay in the switch

</gallery>

==References==
<references>
<ref name="Cherry-MX-spec">Cherry — [http://www.cherrycorp.com/english/switches/key/mx.htm CHERRY MX Series Key Switch]</ref>
<ref name="KPT-102">KBTalking — [http://kbtalking.cool3c.com/article/13939 ★★類ALPS雙藍軸二色KPT-102機械鍵盤★★]</ref>
</references>

[[Category:Keyboard terms]]