Digilent Basys MX3 User manual

1300HenleyCourt
Pullman,WA99163
509.334.6306
www.store.digilent.com
BasysMX3™ Board Reference Manual
RevisedApril21,2017
ThismanualappliestotheBasysMX3rev.B
DOC#: 410-336
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 1of 56
TableofContents
Table of Contents .................................................................................................................. 1
Overview............................................................................................................................... 5
Software Support........................................................................................................................ 6
Coursework and Additional Materials ........................................................................................ 6
1Programming the Board ................................................................................................. 7
1.1 Programming Tools .......................................................................................................... 7
1.2 Programming Basics ......................................................................................................... 8
1.3 Digital Inputs and Outputs ............................................................................................... 9
1.4 Remappable Pins............................................................................................................ 10
1.5 CPU Clock Source ........................................................................................................... 11
2Power Supplies ............................................................................................................ 12
3User LEDs..................................................................................................................... 13
3.1 Connectivity.................................................................................................................... 14
3.2 Functionality................................................................................................................... 14
4User Switches .............................................................................................................. 14
4.1 Connectivity.................................................................................................................... 15
4.2 Functionality................................................................................................................... 16
4.3 Shared Pins..................................................................................................................... 16

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 2of 56
5User Buttons................................................................................................................ 16
5.1 Connectivity.................................................................................................................... 17
5.2 Functionality................................................................................................................... 17
5.3 Shared Pins..................................................................................................................... 18
6RGB LED....................................................................................................................... 18
6.1 Connectivity.................................................................................................................... 19
6.2 Functionality................................................................................................................... 19
6.2.1 RGB LED Implemented Using PWM........................................................................ 19
6.2.2 RGB LED Implemented Using PDM ......................................................................... 20
7Seven-segment Display ................................................................................................ 20
7.1 Connectivity.................................................................................................................... 22
7.2 Functionality................................................................................................................... 23
8LCD Module ................................................................................................................. 24
8.1 Connectivity.................................................................................................................... 25
8.2 Functionality................................................................................................................... 26
9I2C Interface ................................................................................................................. 27
10 Accelerometer ............................................................................................................. 28
10.1 Connectivity................................................................................................................ 28
10.2 Functionality ............................................................................................................... 28
10.3 Shared Pins ................................................................................................................. 29
11 Serial Peripheral Interface............................................................................................ 29
11.1 SPI1 ............................................................................................................................. 29
11.2 SPI2 ............................................................................................................................. 29
12 Flash Memory.............................................................................................................. 30
12.1 Connectivity................................................................................................................ 30

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 3of 56
12.2 Functionality ............................................................................................................... 31
13 UART ........................................................................................................................... 31
13.1 Connectivity................................................................................................................ 32
13.2 Functionality ............................................................................................................... 32
14 Motor Driver................................................................................................................ 32
14.1 Connectivity................................................................................................................ 33
14.2 Functionality ............................................................................................................... 35
15 Servo Headers.............................................................................................................. 35
15.1 Connectivity................................................................................................................ 36
15.2 Functionality ............................................................................................................... 36
15.3 Shared Pins ................................................................................................................. 37
16 IrDA Module ................................................................................................................ 37
16.1 Connectivity................................................................................................................ 37
16.2 Functionality ............................................................................................................... 38
17 Audio Out .................................................................................................................... 39
17.2 Connectivity................................................................................................................ 39
17.2 Functionality ............................................................................................................... 40
18 Microphone ................................................................................................................. 40
18.1 Connectivity................................................................................................................ 41
18.2 Functionality ............................................................................................................... 41
19 Analog Input Control.................................................................................................... 42
19.1 Connectivity................................................................................................................ 42
19.2 Functionality ............................................................................................................... 43
20 Pmod Connectors......................................................................................................... 43

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 4of 56
21 Analog Discovery Debug Header................................................................................... 45
Appendix 1: Remappable Input Pins .................................................................................... 47
Appendix 2: Remappable Output Pins.................................................................................. 49
Appendix 3: Basys MX3 Pinout ............................................................................................ 53

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 5of 56
Overview
The Basys MX3 is a true MCU trainer board designed from the ground up around the teaching experience. Basys
MX3 features the PIC32MX370 from Microchip and was designed to be used with the MPLAB® X IDE. With an
exhaustive set of peripherals, students gain exposure to a wide range of embedded systems related concepts while
using a professional grade tool set. Accompanied by free and open source coursework, including seven in-depth
teaching units and 15 complete labs, the Basys MX3 is a versatile MCU trainer board ideal for teaching introductory
embedded systems courses.
Power:
Switches, Push-buttons, LEDs,
and Displays:
Audio, Motor Control, and Other
Devices:
Powered from USB or
any 5V external power
source
USB and Debugging:
USB-UART Bridge
USB
programmer/debugger
30-pin Analog Discovery
2 connector
5 Push-buttons
1 Reset button
8 Slide switches
8 LEDs
1 RGB LED
4-digit 7-segment display
LCD character display
Expansion Connectors:
Two standard Pmod ports
o16 Total
microcontroller I/O
One I2C Connector
o2 Total
microcontroller I/O
Speaker with Audio Output Jack
and volume control
Microphone with volume
control
Dual H-Bridge Motor Driver for
up to two 1.5 A Brushed DC
Motors or one stepper motor
2 Servo Connectors
FIR-compatible IrDA Module
Potentiometer
3-axis, 12-bit accelerometer
4 MB SPI Flash
The Basys MX3.
PIC32MX370F512L Microcontroller
MIPS32® M4K® core runs up to
96 MHz using onboard 8 MHz oscillator
512 KB of Program Flash Memory, 12 KB
of Boot Flash Memory
128 KB of SRAM
Four Direct Memory Access (DMA)
Modules
Two SPI, Two I²C, and Five UART serial
interfaces
Parallel Master Port (PMP) for graphics
interfaces
Five 16-bit Timers/Counters
Five Input Capture Modules
Five Output Compare Modules
85 I/O pins
o54 pins support Peripheral Pin
Select (PPS) for function
remapping

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 6of 56
SoftwareSupport
The Basys MX3 is fully supported by Microchip’s MPLAB X IDE. See section 1 on Programming the Board for more
information on using the Basys MX3 in MPLAB X IDE. Digilent provides a set of libraries called the Basys MX3
Library Pack that adds support for all onboard peripherals. This library pack can be downloaded from the Basys
MX3 Resource Center.
The Basys MX3 can also be used in Arduino IDE once the Digilent Core for Arduino IDE has been installed.
Instructions for installing the Digilent Core for Arduino IDE can be found on the Basys MX3 Resource Center.
CourseworkandAdditionalMaterials
Basys MX3 comes with a complete set of coursework designed to give teaching professionals flexibility in designing
embedded systems and other microprocessor courses. With almost 300 pages of material, “Embedded Systems
Basys MX3 and PIC32MX370” covers topics from toggling LEDs, motor control, and introduction to digital signal
processing. Access to the full coursework is available on the Basys MX3 Resource Center.
Links to additional materials from Digilent and Microchip, including the Basys MX3 schematic and the
PIC32MX370F512L datasheet, can also be found on the Basys MX3 Resource Center.
The Basys MX3 uses a lot of devices to implement all of the functionality it provides (accelerometer, flash memory,
motor driver, IRDA, etc.). The manufacturers of each of these devices provide detailed descriptions of their
functionality in their datasheets.

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 7of 56
1 ProgrammingtheBoard
1.1 ProgrammingTools
The Basys MX3 can be used with Microchip’s standard MPLAB X IDE. This software suite can be downloaded for
free from the Microchip website and includes a free evaluation copy of the XC32 compiler for use with the PIC32
microcontroller family.
MPLAB X IDE is the tool used to write, compile, program, and debug code running on the Basys MX3 board.
Programming and debugging a program on the Basys MX3 using the MPLAB X IDE is possible using the DEBUG USB
connector. The board contains all the required circuitry for MPLAB X to communicate with the onboard PIC32, so
no additional programming tools need to be purchased.
When creating a new project in MPLAB X, a wizard allows you to setup the environment and device specific tools.
The steps for this include the following:
1. Select Microchip Embedded / Standalone Project, then use the “Select Device” option to specify the PIC32
microcontroller being used: PIC32MX370F512L.
2. Select the programming tool named Basys MX3 corresponding to the board you want to program, under
Licensed Debugger group.
Figure 1.1. MPLAB X tool selection.
3. Select the compiler you want to use.
Figure 1.2. MPLAB X compiler selection.

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 8of 56
Another useful tool included with MPLAB X is MPLAB X IPE. This tool allows the direct programming/erasing of the
microcontroller, but it does not provide an environment for writing, compiling, or debugging the code. Please see
Microchip documentation for instructions on using this tool.
1.2 ProgrammingBasics
It is often very helpful to include the xc.h header when writing code for the Basys MX3:
#include <xc.h>
This further provides the inclusion of another header (p32mx370f512l.h) into the project that provides useful
definitions such as:
Register names
oexample (register LATA is set to 0):
LATA = 0;
Specific register bits that can be accessed using a structure having the name of the register suffixed by
“bits”.
oexample (bit LATA1 of the register LATA is set to 1):
LATAbits.LATA1 = 1;
Digilent provides a set of libraries called the Basys MX3 Library Pack that addresses much of the functionality on
the Basys MX3:
ACL (accelerometer)
ADC (analog-to-digital converter)
AUDIO
BTN (buttons)
IRDA
LCD
LED
MIC (microphone)
MOT (motors)
PMODS
RGBLED
SPIFLASH
SSD
SWT (switches)
UART
These libraries are wrappers over the lower level functions that access the registers, allowing the user to call the
functionality using functions like:
LED_Init();
LED_SetValue(4, 1); //turn on LED4

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 9of 56
This set of libraries comes with the user documentation, but this is what you must do in order to use them:
Include in your project the .c and .h files corresponding to the module you want to use (for example led.c
and led.h).
In your code, include the header of the module:
#include "led.h"
In your code, call the needed functions
1.3 DigitalInputsandOutputs
The PIC32MX370F512L microcontroller offers access to all the board resources through its pins, so understanding
how to access their features is very important. The list that describes each pin functionality is included in Appendix
3. You can see that each pin may have multiple functions, but all pins have one feature in common: they have an
associated digital I/O (input/output) bit. On PIC32 microcontrollers, the I/O pins are grouped into I/O Ports and are
accessed via peripheral registers in the microcontroller. There are seven I/O Ports numbered A–G and each is 16
bits wide. Depending on the PIC32 microcontroller, some of the I/O Ports are not present, and not all 16 bits are
accessible in all I/O Ports.
Each I/O Port has the following control registers: TRIS, LAT, PORT, ANSEL, CNPU, CNPD, and ODC. The registers for
each I/O Port are named after it: TRISx, LATx, PORTx, ANSELx, CNPUx, CNPDx and ODCx. For example, port A will
have the following assigned registers: TRISA, LATA, etc.
The TRIS register is used to set the pin direction. Setting a TRIS bit to 0 makes the corresponding pin an output.
Setting the TRIS bit to 1 makes the pin an input.
The LAT register is used to write to the I/O Port. Writing to the LAT register sets any pins configured as outputs.
Reading from the LAT register returns the last value written.
The PORT register is used to read from the I/O Port. Reading from the PORT register returns the current state of all
the pins in the I/O Port. Writing to the PORT register may not produce the expected result, therefore writing to LAT
register is recommended.
To summarize: write using LAT, read using PORT.
PIC32 microcontrollers allow any pin set as an output to be configured as either a normal digital output or as an
open-drain output. The ODC register is used to control the output type. Setting an ODC bit to 0 makes the pin a
normal output and setting it to 1 makes the pin an open-drain output.
The multifunction pins that include analog input functionality need to be configured in order to be used as digital
pins by clearing the corresponding bit from ANSEL register. These pins will include ANx in their name. For example:
AN11/PMA12/RB11 for RB11.
This microcontroller has a weak pull-up and a weak pull-down connected to each pin. These pull-ups and pull-
downs are enabled/disabled by setting the corresponding bits from CNPU and CNPD registers to 1/0. The default
setting is 0 (pull-ups and pull-downs disabled).
You can see a typical example of I/O pin configuration as output and digital output operations in the User LEDs
section.
You can see a typical example of I/O pin configuration as input (including analog disable) and digital input
operations in the User Buttons section.

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 10 of 56
Refer to the PIC32MX3XX/4XX Family Datasheet, and the PIC32 Family Reference Manual, Section 12, IO Ports, for
more detailed information about the operation of the I/O Ports in the microcontroller.
1.4 RemappablePins
Users may independently map the input and/or output of most digital peripherals to a fixed subset of digital I/O
pins. Pins that support the peripheral pin select feature include the designation “RPn” in their full pin designation,
where “RP” designates a remappable peripheral and “n” is the remappable port number.
The available peripherals to be mapped are digital-only. These include general serial communications (UART and
SPI), general purpose timer clock inputs, timer-related peripherals (input capture and output compare), and
interrupt-on-change inputs.
On the other hand, some peripheral modules cannot be included in the peripheral pin select feature because it
requires special I/O circuitry on a specific port and it cannot be easily connected to multiple pins. These modules
include I2C and analog-to-digital converters (ADC), among others.
Peripheral pin select features are controlled using two sets of Special Function Registers (SFRs): one to map
peripheral inputs, and one to map peripheral outputs.
The peripheral inputs are mapped and named from the peripheral perspective (based on the peripheral). The [pin
name]R registers, where [pin name] refers to the specific peripheral pins, are used to configure peripheral input
mapping. TABLE 12-1 in the PIC32MX370F512L datasheet from Microchip (and Appendix 1 in this document)
shows the different pins and their values available to assign to a peripheral pin.
The following example shows how different I/Os, such as pin RF4, can be assigned to U1RX input pin of the UART1
peripheral:
U1RXR = 0x02; // 0010 corresponds to RF4
Figure 1.3. Remappable input example.
The peripheral outputs are mapped and named from the pin perspective (on the basis of the pin). The RPnR
registers (Register 12-2) are used to control output mapping. The PIC32MX370F512L datasheet details in TABLE 12-
2 (and Appendix 2 in this document) the values corresponding to each IO pin, associated to each available
peripheral pin. Note that the current version of the Basys MX3 schematic (B.0) incorrectly lists RD6 and RD7 as
remappable pins (RPD6 and RPD7, respectively); these pins are not remappable on the PIC32MX370F512L.
The following example shows how different peripheral outputs, such as U3TX, can be assigned to pin RF4:

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 11 of 56
RPF4R = 0x01; // 0001 corresponds to U3TX
Figure 1.4. Remappable output example.
Input and output remapping is illustrated in the SPI2 section, where the SPI2 pins are mapped over the pins of
PMOD A connector.
1.5 CPUClockSource
The PIC32 microcontroller supports numerous clock source options for the main processor operating clock. The
Basys MX3 uses an 8 MHz external crystal for use with the XT oscillator option. Oscillator options are selected via
the configuration settings specified using the #pragma config statement. Use #pragma config
POSCMOD=XT to select the XT option.
Using the internal system clock phase-locked loop (PLL), it is possible to select numerous multiples or divisions of
the 8 MHz oscillator to produce CPU operating frequencies up to 80 MHz. The clock circuit PLL provides an input
divider, multiplier, and output divider. The external clock frequency (8 MHz) is first divided by the input divider
value selected. This is multiplied by the selected multiplier value and then finally divided by the selected output
divider. The result is the system clock, SYSCLK, frequency. The SYSCLK frequency is used by the CPU, DMA
controller, interrupt controller, and pre-fetch cache.
The values controlling the operating frequency are specified using the PIC32MX370 configuration variables. These
are set using the #pragma config statement. Use #pragma config FPLLIDIV to set the input divider,
#pragma config FPLLMUL to set the multiplication factor, and #pragma config FPLLODIV to set the
output divider. Refer to the PIC32MX3XX/4XX Family Datasheet and the PIC32MX Family Reference Manual,
Section Oscillators, for information on how to choose the correct values, as not all combinations of multiplication
and division factors will work.
In addition to configuring the SYSCLK frequency, the peripheral bus clock, PBCLK, frequency is also configurable.
The peripheral bus clock is used for most peripheral devices; particularly the clock used by the timers and serial
controllers (UART, SPI, I2C). The PBLCK frequency is a division of the SYSCLK frequency selected using #pragma
config FPBDIV. The PBCLK divider can be set to divide by 1, 2, 4, or 8.
The following example will set up the Basys MX3 for operation with a SYSCLK frequency of 80 MHz and a PBCLK
frequency of 80 MHz.
#pragma config FNOSC = FRCPLL
#pragma config FSOSCEN = OFF

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 12 of 56
#pragma config POSCMOD = XT
#pragma config OSCIOFNC = ON
#pragma config FPBDIV = DIV_1
#pragma config FPLLIDIV = DIV_2
#pragma config FPLLMUL = MUL_20
#pragma config FPLLODIV = DIV_1
2 PowerSupplies
The Basys MX3 requires a 5V power source to operate. This power source can come from the Programming /
Debugging USB port (J12), the USB-UART (J10), or from an external 5V DC power supply that’s connected to Power
Jack (J11). These three power inputs are connected through Schottky diodes to form the primary input power
network, VIN, which is used to power the onboard regulators and the majority of the onboard peripherals. No
jumper is required to select the input power source. The board will automatically power on while the Power Switch
(SW8) is in the on position and power is present on any of the power inputs.
A power-good LED (LD11), driven by the output of the 3.3V regulator (LMR10515), indicates that the board is
receiving power and that the onboard supplies are functioning as expected. An overview of the Basys MX3 power
circuit is shown in Fig 2.1.
Micro-USB
Port (J10)
UART
Micro-USB
Port (J12)
DEBUG
Power
Jack
(J11)
5V Input
Power On
LED (LD11)
VBAR
VCC3V3
J2
1
DBG_5V0
FT_5V0
J1
1
Servo Headers
JP1
1
Terminal
Block
(J5)
VEXT (0 –11V)
Power
Switch
(SW8)
IC10: LMR10515
1.5AVIN
EN
+-
ON/OFF
IC7: DRV8835
Motor
Driver
VM
VU5V0
IC11: LP2985IM5-3.3
VOUTVIN
ON
VIN
PWR_ON
VIN DBG3V3
Figure 2.1. Power supply circuit.
The USB port(s) can deliver enough power for most designs; however, a few demanding applications, including any
that drive multiple peripheral boards, may require more power than a USB port can provide. In these instances, an
external power supply can be used. Due to their high current demands, motors and servos cannot be powered
through either of the USB ports, and may only be powered through an external supply.

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 13 of 56
An external power supply can be used by plugging into Power Jack J11. The supply must use a coaxial, center-
positive 2.0 mm internal-diameter plug, and provide a voltage of 5V DC (4.75V minimum, 5.5V maximum). The
supply should provide a minimum current of 2A if servos are to be used. Ideally, the supply should be capable of
provide 20 Watts of power (5V DC, 4A). Many suitable supplies can be purchased from Digilent or other catalog
vendors.
The onboard motor driver (Texas Instruments DRV8835) may be powered by a 5V supply connected to Power Jack
J11, or by an external supply (0V-11V) connected to pins 1 and 2 of Terminal Block J5. Jumper JP1 is used to select
which power source is used by the motor driver.
Table 2.1. Power rail characteristics.
3 UserLEDs
Eight LEDs are provided, labeled LD0 –LD7 on the board (and LED0 –LED7 on the schematic), attached to eight
digital I/O pins. Controlling the LEDs is done by basic access to an output I/O pin. Read more details in the Digital
Inputs and Outputs section.
Figure 3.1 shows the way the LEDs are electrically connected on the Basys MX3.
Supply
Circuits
Device
Current (max/typical)
3.3V
(VCC3V3)
PIC32MX370, PMODs, and all
onboard peripherals
excluding the LCD backlight,
RGB LED, IrDA LED, Servos,
and Motors
IC10: Texas Instruments
LMR10515
1.5A/NA
3.3V
(DBG3V3)
Onboard Microchip
Programmer/Debugger
IC11: Texas Instruments
LP2985IM5-3.3
150mA/NA

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 14 of 56
Figure 3.1. LED schematic diagram.
3.1 Connectivity
Label
Schematic
name
PIC32 pin
Description
LD0
LED0
TMS/CTED1/RA0
Led 0
LD1
LED1
TCK/CTED2/RA1
Led 1
LD2
LED2
SCL2/RA2
Led 2
LD3
LED3
SDA2/RA3
Led 3
LD4
LED4
TDI/CTED9/RA4
Led 4
LD5
LED5
TDO/RA5
Led 5
LD6
LED6
TRCLK/RA6
Led 6
LD7
LED7
TRD3/CTED8/RA7
Led 7
Table 3.1. LED connectivity.
All the pins must be defined as digital output (their corresponding TRIS bit must be set to 0):
TRISAbits.TRISA<0-7> = 0; // LED<0-7> configured as output
3.2 Functionality
To turn an LED on or off, turn the corresponding digital output pin high or low by writing 1 or 0 to the
corresponding LATA register bit.
LATAbits.LATA<0-7> = 1; // turn led on
or
LATAbits.LATA<0-7> = 0; // turn led off
Library functions for using the LEDs are contained in the Basys MX3 library pack, LED library; however, the user can
easily use the LEDs without the LED library, as presented above.
4 UserSwitches
Eight switches are provided, labeled SW0 –SW7 on the board and in the schematic, attached to eight digital I/O
pins of the PIC32. Reading the switches is done by basic access to an input I/O pin. Read more details in Digital
Inputs and Outputs section.
Figure 4.1 shows the way the switches are electrically connected on the Basys MX3.

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 15 of 56
Figure 4.1. Switches schematic diagram.
4.1 Connectivity
Label
Schematic
Name
PIC32 Pin
Pin
Shared
With
Description
SW0
SW0
RPF3/RF3
Switch 0
SW1
SW1
RPF5/PMA8/RF5
Switch 1
SW2
SW2
RPF4/PMA9/RF4
Switch 2
SW3
SW3
RPD15/RD15
Switch 3
SW4
SW4
RPD14/RD14
Switch 4
SW5
SW5
AN11/PMA12/RB11
Switch 5
SW6
SW6
CVREFOUT/AN10/RPB10/CTED11PMA13/RB10
Switch 6
SW7
SW7
AN9/RPB9/CTED4/RB9
TRIG_2
Switch 7
Table 4.1. Switches connectivity.
All the pins must be defined as digital input: their corresponding TRIS bit must be set to 1, and analog function
must be disabled for pins routed to SW5, SW6, and SW7.
TRISFbits.TRISF3 = 1; // RF3 (SW0) configured as input
TRISFbits.TRISF5 = 1; // RF5 (SW1) configured as input
TRISFbits.TRISF4 = 1; // RF4 (SW2) configured as input
TRISDbits.TRISD15 = 1; // RD15 (SW3) configured as input
TRISDbits.TRISD14 = 1; // RD14 (SW4) configured as input
TRISBbits.TRISB11 = 1; // RB11 (SW5) configured as input
ANSELBbits.ANSB11 = 0; // RB11 (SW5) disabled analog
TRISBbits.TRISB10 = 1; // RB10 (SW6) configured as input
ANSELBbits.ANSB10 = 0; // RB10 (SW6) disabled analog

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 16 of 56
TRISBbits.TRISB9 = 1; // RB9 (SW7) configured as input
ANSELBbits.ANSB9 = 0; // RB9 (SW7) disabled analog
4.2 Functionality
In order to read the switches, the user needs to read the corresponding digital input pin. A value of 1 indicates the
switch as being on (high) or 0 indicates the switch as being off (low).
val = PORTFbits.RF3; // read SW0
val = PORTFbits.RF5; // read SW1
val = PORTFbits.RF4; // read SW2
val = PORTDbits.RD15; // read SW3
val = PORTDbits.RD14; // read SW4
val = PORTBbits.RB11; // read SW5
val = PORTBbits.RB10; // read SW6
val = PORTBbits.RB9; // read SW7
Library functions for using the switches are contained in the Basys MX3 library pack, SWT library; however, the
user can easily use the switches without the SWT library, as presented above.
4.3 SharedPins
As shown in the connectivity table above, SW7 driving signal is shared with the TRIG_2 signal in 2x15 pins Debug
Header.
5 UserButtons
There are five buttons on the board, labeled BTNU, BTNL, BTNC, BTNR, BTND both on the board and in the
schematic, attached to five digital I/O pins of PIC32. Reading the buttons is done by basic access to an input I/O
pin. Read more details in Digital Inputs and Outputs section.
Figure 5.1 shows the way the buttons are electrically connected on the Basys MX3.

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 17 of 56
Figure 5.1. Button schematic diagram.
The Basys MX3 also has a red button labeled RESET. This button is connected directly to the MCLR pin of the PIC32
and will trigger it to be reset.
5.1 Connectivity
Label
Schematic
Name
PIC32 Pin
Pin Shared
With
Description
BTNU
BTNU
PGEC1/AN1/RPB1/CTED12/RB1
PGC
Button up
BTNL
BTNL
PGED1/AN0/RPB0/RB0
PGD
Button left
BTNC
BTNC
RPF0/PMD11/RF0
TRIG_1
Button center
BTNR
BTNR
AN8/RPB8/CTED10/RB8
S0_PWM
Button right
BTND
BTND
RPA15/RA15
S1_PWM
Button down
Table 5.1. Button connectivity.
All the pins must be defined as digital input: their corresponding TRIS bit must be set to 1, and analog function
must be disabled for pins corresponding to BTNU, BTNL, BTNR, BTND.
TRISBbits.TRISB1 = 1; // RB1 (BTNU) configured as input
ANSELBbits.ANSB1 = 0; // RB1 (BTNU) disabled analog
TRISBbits.TRISB0 = 1; // RB1 (BTNL) configured as input
ANSELBbits.ANSB0 = 0; // RB1 (BTNL) disabled analog
TRISFbits.TRISF4 = 1; // RF0 (BTNC) configured as input
TRISBbits.TRISB8 = 1; // RB8 (BTNR) configured as input
ANSELBbits.ANSB8 = 0; // RB8 (BTNR) disabled analog
TRISAbits.TRISA15 = 1; // RA15 (BTND) configured as input
5.2 Functionality
To read the buttons, the user needs to read the corresponding digital input pin, a value of 1 indicating the button is
pressed or 0 indicating the button is released:

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 18 of 56
val = PORTBbits.RB1; // read BTNU
val = PORTBbits.RB0; // read BTNL
val = PORTFbits.RF0; // read BTNC
val = PORTBbits.RB8; // read BTNR
val = PORTAbits.RA15; // read BTND
Please note that if you want the buttons to trigger a specific functionality, proper software debouncing is required.
Library functions for using the buttons are contained in the Basys MX3 library pack, BTN library; however, the user
can easily use the buttons without the BTN library, as presented above.
5.3 SharedPins
As shown in the connectivity Table 5.1 above, some pins are shared:
Buttons BTNL and BTNU share functions with PGD and PGC signals used for programming. Therefore, the
following line should be inserted in the code, to disable their programming function.
#pragma config JTAGEN = OFF
Buttons BTNR and BTND share the pins with S0_PWM and S1_PWM, explained in Servo headers section,
so these resources should be used exclusively.
BTNC is shared with TRIG_1 signal in 2x15 Pins Debug Header, so it can be used to trigger events in an
Analog Discovery board experiment.
6 RGBLED
The Basys MX3 board contains one tri-color (RGB) LED. The LED allows the user to obtain any RGB color by
configuring the R, G and B color components.
Figure 6.1. RGB LED schematic diagram.
The usage of the RGB LED is the same as controlling three separate LEDs, one for each color. Figure 6.1 shows the
way the RGB LED is electrically connected on the Basys MX3.

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 19 of 56
There is one digital signal to control each color component. Using either 0 or 1 values for these signals will only
give the user a limited number of colors (two colors for each component), so most of the time this is not enough in
applications using the RGB feature. The solution is to send a sequence of 1 and 0 values on these digital lines,
switched rapidly with a frequency higher than human perception. The “duty factor” will finally determine the
color, as the human eye will “integrate” the discrete illumination values into the final color sensation.
The most used approach in solving this problem is the use of pulse-width modulation (PWM) signals. Another
approach is the use of pulse-density modulation (PDM). These methods are explained in the RGB LED Implemented
Using PWM and RGB LED Implemented Using PDM sections.
6.1 Connectivity
Label
Schematic
Name
PIC32 Pin
Description
R
LED8_R
AN25/RPD2/RD2
Signal corresponding to the R component of
the RGB
G
LED8_G
RPD12/PMD12/RD12
Signal corresponding to the G component of
the RGB
B
LED8_B
AN26/RPD3/RD3
Signal corresponding to the R component of
the RGB
Table 6.1. RGB LED connectivity.
6.2 Functionality
6.2.1 RGBLEDImplementedUsingPWM
The percentage of each period that the pulse is high determines the signals “duty cycle”. Figure 6.2 shows how
different duty cycles are implemented using PWM.
Figure 6.2. PWM duty cycle.
Using this method, the intensity of each component of the RGB LED is determined by the duty cycle being applied.
PWM is most often implemented in the microcontroller using the output compare (OC) peripheral modules along
with a timer.
One timer (Timer y) is assigned to the OC module. Setting the PRy register of the timer will set the PWM period.
Setting the OCxRS register of the OC module will set the actual duty cycle.
The PIC32 datasheet displayed in Fig. 6.3 below explains how one period of the PWM is generated.

Basys MX3™ Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 20 of 56
Figure 6.3. PIC32 PWM generation.
The RGBLED library from the Basys MX3 library pack contains a commented example of PWM implementation with
the following features:
LED8_R, LED8_G, and LED8_B are mapped to OC3, OC5, and OC4.
OC3, OC5, and OC4 are properly configured, together with assigned Timer 2.
When a new color is set, its components (R, G, and B) are assigned to OC3RS, OC5RS, and OC4RS.
6.2.2 RGBLEDImplementedUsingPDM
PDM method adjusts both the frequency and length of the “High” pulses in the modulated signal.
A PDM is implemented using a register and an accumulator adder with carry output. The n-bit register can store
any binary value from 0 to 2𝑛− 1. In each clock period, the register content is added to the accumulator. The carry
bit (overflow of the n-bit accumulator) is the output. It is “High” as often as the accumulator overflows, so that
when large values are added, carry will occur often. The “High” pulse is only 1 clock period long, but more “High”
pulses can succeed when the register content is close to maximum.
The RGBLED library from the Basys MX3 library pack contains an example of PDM implementation, with the
following features:
LED8_R, LED8_G, and LED8_B are configured as simple digital outputs.
Timer 5 is configured to generate an interrupt every approx. x us.
Three 16-bit accumulators are used, one for each color.
In the interrupt service routine, for each color, the 8-bit color value is added to the corresponding 16-bit
accumulator.
For each color, the 9th bit of the accumulator is considered the carry bit. The resulted carry bits are
assigned to LED8_R, LED8_G, and LED8_B.
For each color, the accumulator is masked so that it only contains an 8-bit value (carry is cleared).
7 Seven-segmentDisplay
The Basys MX3 board contains a four-digit common anode seven-segment LED display. Each of the four digits is
composed of seven segments displaying a “figure 8” pattern and a decimal point with an LED embedded in each
segment. Segment LEDs can be individually illuminated. Of the number of possible patterns, the ten corresponding
to the decimal digits are the most useful.