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PmodJSTK™ Reference Manual
Revised May 24, 2016
This manual applies to the PmodJSTK rev. C
Overview
The PmodJSTK is designed to be a versatile peripheral module that can be used in a wide variety of projects. It
contains a resistive twin axis joystick that includes a center push button along with two additional push buttons.
The PmodJSTK also has two programmable LEDs located on the board that can provide additional information to
the user.
The PmodJSTK is ideally suited for Digilent microcontroller or FPGA based projects that require proportional
control from the user, such as robotic applications.
Features include:
The PmodJSTK.
2-axis resistive joystick with central push
button
Two additional user push buttons
Two user indicator LEDs
Small PCB size for flexible designs 1.8“ ×
1.3” (4.6 cm × 3.3 cm)
6-pin Pmod connector with SPI interface
Follows
Digilent Pmod Interface
Specification
Type 2
Library and example code available
in
resource center
1
Functional Descriptions
The PmodJSTK uses an
Atmel® ATtiny24 microcontroller
in a MLF20 package to collect information about its
peripherals. The twin axis joystick uses two potentiometers to measure the current position in the x and y
coordinate directions and stores the information in two 10-bit values ranging from 0 to 1023.
2
Interfacing with the Pmod
The PmodJSTK communicates with the host board via the SPI communication protocol in 5 byte chunks. The first
four bytes correspond to the two 10-bit values representing the X and Y coordinate directions and the last byte
DOC#: 502-116
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PmodJSTK™ Reference Manual
indicates the status of the three push buttons. Details on the organization of these bytes are provided a little
further down in this document.
The PmodJSTK will send its total of 23 bits of information to the system board through 40 clock cycles. The first two
bytes received will consist of the 10-bit position of the potentiometer in the x-direction (with the Pmod arranged
so that the pin header is facing "up"). The lower 8 bits of this 10-bit value will arrive MSB in the first byte and the
remaining two MSB of the 10-bit value will arrive as the last two bits in the second byte.
Similarly, the 10-bit position of the potentiometer in the y-direction (with the Pmod arranged so that the pin
header is facing "up"). The lower 8 bits of this 10-bit value will arrive MSB in the third byte and the remaining two
MSB of the 10-bit value will arrive as the last two bits in the fourth byte.
The three bits representing the three push buttons arrive as the last three bits in the fifth byte where a '1'
indicates that the button is pressed and a '0' indicates that the button is not being pressed. The organization of the
button bits (as labeled on the silk screen of the Pmod) are arranged as follows in the fifth byte.
The overall order of bytes that will be sent by the
PmodJSTK
to the system board will be as follows:
1
X (low)
2
X (high)
3
Y (low)
4
Y (high)
5
Buttons
Table 1. Byte order sent by the PmodJSTK to the system board.
As per the SPI protocol, the system board also needs to send five bytes of information to the Pmod. The first byte
will contain information indicating if the two on-board LEDs should be turned on or off with the remaining four
bytes ignored by the PmodJSTK. The last two bits of the first byte sent indicate the status LED2 and LED1,
respectively.
A pinout table for the PmodJSTK is provided below:
Pin
1
2
3
4
5
6
Signal
~CS
MOSI
MISO
SCK
GND
VCC
Description
Chip Select (active low)
Master-Out-Slave-In
Master-In-Slave-Out
Serial Clock
Power Supply Ground
Power Supply (3.3V/5V)
Table 2. Pin descriptions for the PmodJSTK.
Any external power applied to the PmodJSTK must be within 2.7V and 5.5V; however, it is recommended that the
Pmod is operated at 3.3V.
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Other product and company names mentioned may be trademarks of their respective owners.
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PmodJSTK™ Reference Manual
3
Physical Dimensions
The pins on the pin header are spaced 100 mil apart. The PCB is 1.8 inches long on the sides parallel to the pins on
the pin header and 1.3 inches long on the sides perpendicular to the pin header.
4
Additional Information
For the most up-to-date reference material, visit Digilent's Wiki at
reference.digilentinc.com.
The schematics of the
PmodJSTK are available
here.
Additional information about the Atmel ATtiny24 can be found at
atmel.com.
Example code demonstrating how to get information from the PmodJSTK can be found
here.
If you have any questions or comments about the PmodJSTK, feel free to post them under the appropriate section
("Add-on Boards") of the
Digilent Forum.
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
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