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PmodENC™ Reference Manual
Revised April 12, 2016
This manual applies to the PmodENC rev. A
Overview
The Digilent PmodENC features a rotary shaft encoder with an integral push-button to provide multiple types of
outputs. The module also includes a sliding switch that is commonly used as an on/off output. An encoder is
commonly used in freely rotating volume knobs to detect how many “clicks” a knob has been rotated.
Features include:
The PmodENC.
Rotary push-button shaft encoder
Add multiple types of user input to host
board or project
Additional static slide switch
Small PCB size for flexible designs 1.5 in ×
0.8 in (3.8 cm × 2.0 cm)
6-pin Pmod port with GPIO interface
Follows Digilent Pmod Interface
Specification Type 1
Library and example code available
in
resource center
1
Functional Description
The PmodENC utilizes a rotary shaft encoder as a way for users to quickly switch between multiple options such as
choices shown on a screen or predefined motors speeds. An integral push-button on the shaft as well as a slide
switch allow for a highly configurable Pmod.
2
Interfacing with the Pmod
The PmodENC communicates with the host board via the GPIO protocol. It provides four inputs to the system
board; the two buttons internal to the encoder that are in quadrature with each other as well as the integral push
button on the shaft and the slide switch. A system board will read the integral push button and the slide switch at
a logic low voltage in their native (or off in the case of the switch) states.
DOC#: 502-117
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
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PmodENC™ Reference Manual
The two internal buttons are both natively pulled to a logic high level through a pull-up resistor. As the two buttons
are located 90 degrees from each other (i.e. in quadrature), while the shaft is rotating one button will be pulled to
a low logic level voltage before the other button.
Figure 1. Rotary shaft encoder circuitry.
Users can program their system boards to determine which button was pulled low last (within a small time frame
to ensure additional “clicks” are not also captured) in order to figure out which direction the shaft is being rotated.
Switch Chatter
Rotate Right
A
B
Rising edge of A first, then B
is decoded as a rotate right
Figure 2. Timing of outputs A and B.
2.1
Pinout Description Table
Pin
1
2
3
4
5
6
Signal
A
B
BTN
SWT
GND
VCC
Description
Output of button A in the encoder shaft
Output of button B in the encoder shaft
Output of the integral push button in the encoder shaft
Output of the on board switch
Power Supply Ground
Positive Power Supply (3.3/5V)
It is recommended that Pmod is operated at 3.3V or 5V, although because there are no integrated circuits on the
Pmod, any voltage that your system board can handle as a digital input will work fine.
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Detent
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PmodENC™ Reference Manual
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Physical Dimensions
The pins on the pin header are spaced 100 mil apart. The PCB is 1.5 inches long on the sides parallel to the pins on
the pin header and 0.8 inches long on the sides perpendicular to the pin header.
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
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