p p m m o o d d e e n n c c ? ? r r e e f f e e r r e e n n c c e e m m a a n n u u a a l l revision: october 31, 2011 note: this document applies to rev a of the board. 1300 ne henley court, suite 3 pullman, wa 99163 (509) 334 6306 voice | (509) 334 6300 fax doc: 502-117 page 1 of 2 copyright digilent, inc. all rights reserved. other product and company names mentioned may be tradema rks of their respective owners. overview the pmodenc rotary encoder module features a rotary shaft encoder with integral push-button that provides rotate-right, rotate- left, and button-press outputs. the module also includes a sliding switch that provides an on/off output. features include: ? a rotary push-button shaft encoder ? a slide switch with a series resistor ? a 6-pin header ? small form factor (1.5? x 0.75?). functional description there are four outputs on the pmodenc module, labeled a, b, btn, and swt. outputs a and b are the encoded outputs from the rotary shaft encoder. in principle, the rotary shaft encoder behaves like a cam connected to a central shaft. rotating the shaft operates two push-button switches, as shown in figure 2. depending on which way the shaft is rotated, one of the switches closes before the other. likewise, as the rotation continues, one switch opens before the other. when the shaft is stationary (the detent position) both switches are open (logic 1). 5 = gnd 1 = a 2 = b 3 = btn 4 = swt 6 = vcc figure 1 pmodenc pin signals figure 2 rotary shaft encoder circuitry
pmodxyz reference manual www.digilentinc.com page 2 of 2 copyright digilent, inc. all rights reserved. other product and company names mentioned may be tradema rks of their respective owners. pressing the rotary push-button shaft encoder will drive the output pin btn to vcc voltage or a logic level 1. otherwise btn is driven to gnd voltage or a logic level 0. placing the slide switch into the up position on the pmodenc module will drive the output swt to vcc voltage or a logic level 1. placing the slide switch in the down position will drive swt to gnd voltage or a logic level 0. decoding rotations of the rotary shaft figure 4 shows a timing diagram of a rotate- right on the rotary push-button shaft of the pmodenc module. note the logic noise shown with opening and closing of the switches. a rotate-left of the rotary push-button shaft is similar to figure 4. the only difference is that output b will drop to logic level 0 first, followed by output a. figure 3 push-button circuitry detent figure 4 timing of outputs a and b
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