Digilent chipKIT wf32 Reference Manual

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chipKIT™ WF32™ Board Reference Manual

Revised September 16, 2013 This manual applies to the chipKIT WF32 rev. B

DOC#: 502-273

Other product and company names mentioned may be trademarks of their respective owners.

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The chipKIT WF32 board.

 Microchip® PIC32MX695F512L microcontroller (80

MHz 32-bit MIPS, 512K Flash, 128K SRAM)

 Microchip MRF24WG0MA WiFi module  microSD card connector  USB 2.0 OTG controller with A and micro-AB

connectors

 43 available I/O pins  Four user LEDs  PC connection uses a USB A to mini-B cable (not

included)

 12 analog inputs  3.3V operating voltage  80 MHz operating frequency  7V to 15V input voltage (recommended)  30V input voltage (maximum)  0V to 3.3V analog input voltage range  High efficiency, switching 3.3V power supply

providing low-power operation

Overview

The chipKIT WF32 is based on the popular Arduino™ open-source hardware prototyping platform and adds the performance of the Microchip PIC32 microcontroller. The WF32 is the first board from Digilent to have a WiFi MRF24 and SD card on the board both with dedicated signals. The WF32 board takes advantage of the powerful PIC32MX695F512L microcontroller. This microcontroller features a 32-bit MIPS processor core running at 80Mhz, 512K of flash program memory, and 128K of SRAM data memory.

The WF32 can be programmed using the Multi-Platform Integrated Development Environment (MPIDE), an environment based on the original Arduino IDE, modified to support PIC32. It contains everything needed to start developing embedded applications. The WF32 features a USB serial port interface for connection to the MPIDE and can be powered via USB or by an external power supply. In addition, the WF32 is fully compatible with the advanced Microchip MPLAB® IDE and works with all MPLAB compatible in-system programmer/debuggers, such as

the Microchip PICkit™3 or the Digilent chipKIT PGM. The WF32 is easy to use and suitable for both beginners and

advanced users experimenting with electronics and embedded control systems.

chipKIT™ WF32™ Board Reference Manual

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5 6

Call Out

Component Description

Call Out

Component Description

IC3- Microchip MRF24WG0MA WiFi Module

J13- USB Connectors

User Buttons

JP9- USB Overcurrent Detect

JP3- Microchip Debug Tool Connector

JP11- Hos USB Bus Power Enable

J6-  Signals

J8- Analog and Digital Signal Connector

BTN1- Reset

JP5, JP4- Analog or C Select Jumper

JP1- Reset Disable

J3- Shield Power Connector

J9- Digital Signal Connector

J16- 5.0V Supply Select

JP3- Pin 10 Signal Select Jumper

J15- Power Select Jumper

PIC32 Microcontroller

J11- Micro SD Connector

Potentiometer

J17- External Power Connector

J7- Digital Signal Connector

J14- External Power Connector

1 ChipKIT WF32 Hardware Overview

The WF32 has the following hardware features:

chipKIT™ WF32™ Board Reference Manual

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User LEDs

J2- USB- UART Handshaking Signals

JP6,7- SPI Master/ SPI Slave Select

USB connector for USB Serial Converter

J10- SPI Connector

Serial Communication LEDs

JP10- USB Host or OTG Select

2 MPIDE and USB Serial Communications

The WF32 board is designed to be used with MPIDE. The MPIDE development platform was created by modifying the Arduino IDE. It is backwards-compatible with the Arduino IDE. Links for where to obtain the MPIDE installation files and instructions for installing MPIDE can be found at www.chipkit.net/started.

The MPIDE uses a serial communications port to communicate with a boot loader running on the WF32 board. The serial port on the WF32 board is implemented using an FTDI FT232RQ USB serial converter. Before attempting to use the MPIDE to communicate with the WF32, the appropriate USB device driver must be installed.

The WF32 board uses a standard mini-USB connector. Generally, a USB A to mini-B cable is used for connection to a USB port on the PC.

When the MPIDE needs to communicate with the WF32 board, the board is reset and starts running the boot loader. The MPIDE then establishes communications with the boot loader and uploads the program to the board.

When the MPIDE opens the serial communications connection on the PC, the DTR pin on the FT232RQ chip is driven low. This pin is coupled through a capacitor to the MCLR pin on the PIC32 microcontroller. Driving the MCLR line low resets the microcontroller, which restarts the execution with the boot loader.

This automatic reset action (when the serial communications connection is opened) can be disabled. To disable this operation, there is a jumper labeled JP1, which can be disconnected. JP1 is normally shorted, but if the shorting block is removed, the automatic reset operation will be disabled.

Two red LEDs (LD1 and LD2) will blink when data is being sent or received between the WF32 and the PC over the serial connection.

The header connector J2 provides access to the other serial handshaking signals provided by the FT232RQ. Connector J2 is not loaded at the factory and can be installed by the user to access these signals.

3 Power Supply

The WF32 is designed to be powered via USB (J1), from an external power supply (J14 or J17), or from the USB OTG receptacle (J12). Jumper block J15 is used to select which power supply is used. The power supply voltage selected by J15 is applied to the unregulated power bus, VU.

In order to operate the WF32 as a USB device powered from the USB serial interface, connector J1, place a shorting block in the UART position of jumper block J15. To operate the WF32 from an external power supply,

chipKIT™ WF32™ Board Reference Manual

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LDO OutLDO In

VU 5V0

GNDEN Ext

attach the power supply to either J14 or J17 and place a shorting block in the EXT position of J15. Be sure to observe correct polarity when connecting a power supply to J14, as a reversed connection could damage the board. To operate the WF32 as a USB powered device from the USB OTG connector (J12) place a shorting block on the USB position of J15. This will normally only be done when running a sketch on the board that programs it to operate as a USB device. The power supply section in the WF32 provides two voltage regulators, a 3.3V regulator and a 5V regulator. All systems on the WF32 board itself operate at 3.3V and are powered by the 3.3V regulator. The 5V regulator is used to provide power for external circuits, such as shields, that require 5V for operation. The 5V regulator can be completely disabled if it is not needed for a given application.

The WF32 board is designed for low power operation and efficient use of battery power, as such a switch mode voltage regulator is used for the 3.3V power supply. This switch mode regulator is made up of a Microchip MCP16301 and associated circuitry. It can operate on input voltages from 4V to 30V with up to 96% efficiency, and is rated for 600mA total current output. The MCP16301 has internal short circuit protection and thermal protection. The 3.3V regulator takes its input from the unregulated power bus, VU, and produces its output on the VCC3V3 power bus. The VCC3V3 bus provides power to all on-board systems and is available at the shield power connector (J3) to provide 3.3V power to external circuitry, such as shields.

The 5V regulator section provides a low dropout linear regulator. No circuitry on the WF32 board uses the 5V supply. It is provided for powering external circuitry that needs a 5V power supply. This voltage regulator uses an On Semiconductor NCP1117LP. The NCP1117LP is rated for an output current of 1A. The dropout voltage of the NCP1117LP is a maximum of 1.4V at 1A output current. The maximum input voltage of the NCP1117LP is 18V. The recommended maximum operating voltage is 15V.

The input voltage to the 5V regulator section is taken from the VU bus, and the output is placed on the VCC5V0 power bus.

There is a reverse polarity protection diode in the external power supply circuit. Considering the diode drop plus the forward drop across the regulator, the minimum input voltage to the regulator should be 7V to produce a reliable 5V output.

For input voltages above 9V, the regulator will get extremely hot when drawing high currents. The NCP1117LP has output short circuit protection and internal thermal protection and will shut down automatically to prevent damage.

The 5V regulator section actually provides four 5V power options:

1) 5V regulator completely disabled and no 5V power available;

2) 5V regulator bypassed and 5V provided from an external 5V power supply, such as USB;

3) on-board 5V regulator used to provide 5V power;

4) External 5V regulator used to regulate VU and provide 5V power.

Jumper block J16 is used to select these various options and the following diagrams describe the use of J16:

This diagram shows the arrangement of the signals on J16:

LDO In is the input to the on-board linear regulator.

LDO Out is the output of the on-board linear regulator

chipKIT™ WF32™ Board Reference Manual

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LDO OutLDO In

VU 5V0

GNDEN Ext

LDO OutLDO In

VU 5V0

GNDEN Ext

VU is the unregulated input voltage selected by the jumper setting jumper block J15.

5V0 is the connection to the VCC5V0 power bus on the WF32 board.

EN Ext is a signal provided to enable an external voltage regulator if one is being used. This would allow the sketch running on the WF32 to turn on/off the external voltage regulator. When used with an external voltage regulator, this allows the board to go into an extremely low power operating mode. This signal is connected to Port D, bit 13 (RD13) on the PIC32 microcontroller. This is accessible using digital pin 64.

GND is a connection to the digital ground bus on the WF32 board.

To completely disable operation of the on-board linear regulator, remove all shorting blocks from J16.

To use the on-board 5V regulator, use the provided shorting blocks to connect VU to LDO In, and to connect LDO Out to 5V0, as follows:

Note: In this case, when J15 is in the EXT position, and J16 is jumpered to regulate the external input, do not apply more than 18V. This can destroy the 5.0V regulator.

To bypass the on-board 5V regulator when powering the board from an externally regulator 5V power supply, such as USB, Use one of the provided shorting blocks to connect VU to 5V0, as follows:

An external 5V regulator can be used. This would be desirable, for example, when operating from batteries. An external switch mode 5V regulator could be used to provide higher power efficiency than the on-board linear regulator. In this case, use wires as appropriate to connect VU to the unregulated input of the external regulator. Connect the regulated 5V output to 5V0. Connect GND to the ground connection of the external regulator. Optionally, connect EN Ext to the enable input control of the external regulator, if available. This allows the external regulator to be turned off for low power operation. Digital pin 64 is then used to turn on/off the external regulator.

The PIC32MX695 microcontroller is rated to use a maximum of 98mA of current when operating at 80Mhz. The MRF24WG0MA WiFi module typically consumes a maximum of 237mA when transmitting. This allows approximately 265mA of current to power the remaining 3.3V circuitry on the WF32 board and external circuitry powered from the VCC3V3 bus. No circuitry on the WF32 board is powered from the VCC5V0 power bus, leaving all current available from the 5V regulator to power external circuitry.

The POWER connector (J3) is used to power shields connected to the WF32 board. Pin 1 is unconnected, the following pins are provided on this connector:

IOREF (pin 2): This pin is tied to the VCC3V3 bus.

P32_RST (pin 3): This connects to the MCLR pin on the PIC32 microcontroller and can be used to reset the PIC32.

VCC3V3 (pin 4): This routes the 3.3V power bus to shields.

VCC5V0 (pin 5): This routes the 5V power bus to shields.

chipKIT™ WF32™ Board Reference Manual

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GND (pin 6, 7): This provides a common ground connection between the WF32 and the shields. This common ground is also accessible on connectors J4 and J5.

VEXT (pin 8): This connects to the voltage provided at the external power supply connectors (J14 and J17). This can be used to provide unregulated input power to the shield. It can also be used to power the WF32 board from the shield instead of from the external power connector.

4 5V Compatibility

The PIC32 microcontroller operates at 3.3V. The original Arduino boards operate at 5V, as do many Arduino shields.

There are two issues to consider when dealing with 5V compatibility for 3.3V logic. The first is protection of 3.3V inputs from damage caused by 5V signals. The second is whether the 3.3V output is high enough to be recognized as a logic high value by a 5V input.

The digital I/O pins on the PIC32 microcontroller are 5V tolerant. The analog capable I/O pins are not 5V tolerant. To provide 5V tolerance on those pins, the WF32 contains clamp diodes and current limiting resistors to protect them from 5V input voltages.

The fact that all I/O pins are 5V tolerant means that it is safe to apply 5V logic levels to any pins on the board without risk of damaging the PIC32 microcontroller.

The minimum high-voltage output of the PIC32 microcontroller is rated at 2.4V when sourcing 12mA of current. When driving a high impedance input (typical of CMOS logic) the output high voltage will be close to 3.3V. Some 5V

devices will recognize this voltage as a logic high input, and some won’t. Many 5V logic devices will work reliably

with 3.3V inputs.

5 Input/ Output Connections

The WF32 board provides 43 of the I/O pins from the PIC32 microcontroller at pins on the input/output connectors J6, J7, J8, J9, and J10.

The PIC32 microcontroller can source or sink a maximum of 25mA on all digital I/O pins. However, to keep the output voltage within the specified output voltage range (VOL 0.4V, VOH 2.4V) the pin current must be restricted to +7/-12mA. The maximum current that can be sourced or sunk across all I/O pins simultaneously is +/-200mA. The maximum voltage that can be applied to any I/O pin is 5.5V although not all pins are 5V tolerant. For more detailed specifications, refer to the PIC32MX5XX/6XX/7XX Data Sheet available from www.microchip.com.

Note that the series resistors that are part of the voltage clamp circuit to provide 5V tolerance on the analog capable I/O pins, limiting the current that can be sourced or sunk by those pins. These resistors add 200 ohms of resistance to the input/output circuit and limit the effective drive current to about 1mA-2mA source/sink capability on the analog capable pins.

Connectors J7 and J9 are 2x8 female pin header connectors that provide digital I/O signals. The outer row of pins (closer to the board edge) corresponds to the I/O connector pins on an Arduino Uno or Duemilanove board. The inner row of pins provides access to the extra I/O signals provided by the PIC32 microcontroller.

Connector J8 is a 2x6 female pin header connector that provides access to the analog input pins on the microcontroller. The outer row of pins corresponds to the six analog pins on an Arduino Uno or Duemilanove. The inner row of pins is for the additional I/O signals provided by the PIC32 microcontroller. The analog pins on J8 can also be used as digital I/O pins.

chipKIT™ WF32™ Board Reference Manual

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The chipKIT/Arduino system uses logical pin numbers to identify digital I/O pins on the connectors. The logical pin numbers for the I/O pins on the WF32 are 0-48. These pin numbers are labeled in the silk screen on the board.

Pin numbers 0-13 are the outer row of pins on J9 and J7, from right to left. Pin numbers 14-19 are the outer row of pins on J8 from left to right. Pins 20-25 are the inner row of pins on J8 from left to right. Pin numbers 26-41 are the inner row of pins on J9 and J7 from right to left. Pin 42 is the pin labeled A on J7. This pin is normally the reference voltage for the microcontroller’s A/D converter, but can also be used as a digital I/O pin.

In addition to the connector pin, Pin 13 also connects to the user LED LD3. Pin 43 connects to user LED LD5. Pin 43 does not attach to any connector. Pin 44 is the SS signal for SPI port 2, and discussed more in the SPI section below. Pins 45 and 46 are intended to be used for I2C and are connected to the 2x1 female header connector, J6. Pins 47 and 48 connect to the user LEDs LD5 and LD6.

The analog inputs on connector J8 are assigned pin numbers. The outer row of pins on J8 is analog inputs A0-A5. The inner row of pins is A6-A11. These pins are also assigned digital pin numbers; A0-A5 are digital pins 14-19, and A6-A11 are 20-25.

6 802.11b/g Interface

The 802.11b/g compatible WiFi interface on the WF32 is provided by a Microchip MRF24WG0MA WiFi module. This module provides the radio transceiver, antenna, and 802.11 compatible network firmware.

The MRF24WG0MA firmware provides the 802.11 network protocol software support. The DNETcK and DWIFIcK libraries provide the TCP/IP network protocol support that works with the 802.11 protocol support provided by the WiFi module.

The primary communications interface with the MRF24WG0MA WiFi module is a 4 wire SPI bus. This SPI bus uses SPI4 in the PIC32 microcontroller, and this SPI controller is dedicated to use for communications with the WiFi module.

The WiFi module supports SPI clock speeds up to 25MHz. In addition to the SPI interface, the interface to the WiFi module also includes a reset signal, an interrupt signal and a hibernate signal. The active low RESET signal is used to reset the WiFi module The external interrupt signal, INT, is used by the module to signal to the host microcontroller that it needs servicing by the microcontroller software. The INT signal on the WiFi module is connected to external interrupt INT4 on the PIC32 microcontroller. The active low HIBERNATE signal is used to power the WiFi module down and put it into a low power state.

The interface signals to the WiFi module are controlled by the network libraries and are not normally accessed by the user sketch. Refer to the schematic for the WF32 board for details on these connections.

More detailed information about the operation of the MRF24WG0MA can be obtained from the manufacturer data sheet available from www.microchip.com.

7 Network Library Software

The WiFi module on the WF32 is intended for use with the Digilent chipKIT network libraries DNETcK and DWIFIcK. The DNETcK library provides TCP/IP protocol support for all chipKIT compatible network interfaces supported by Digilent products, including the WF32. The DWIFIcK library provides the additional library support required for connecting to and operating with the Microchip MRF24WG0MA wireless network modules.

chipKIT™ WF32™ Board Reference Manual

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The DWIFIcK library supports both the MRF24WB0MA and MRF24WG0MA modules. The correct header file must be used to specify the network hardware being used by the sketch. When writing a network sketch on the WF32, use the following hardware library:

#include <WiFiShieldOrPmodWiFi_G.h>

The Digilent chipKIT network libraries are available for download from the Digilent web site: www.digilentinc.com. These libraries make use of a custom version of the Microchip Application Library. It is necessary to accept the Microchip Application Library license agreement before downloading the library.

There are reference examples demonstrating the use of these libraries in the library download. There are more extensive examples available on the Digilent web site as well.

8 USB Interface

The PIC32MX695 microcontroller on the WF32 contains a USB 2.0 Compliant, Full Speed Device and On-The-Go (OTG) controller. This controller provides the following features:

 USB full speed host and device support.  Low speed host support.  USB OTG support.  Endpoint buffering anywhere in system RAM.  Integrated DMA to access system RAM and Flash memory.

Connector J13 on the top right side of the board is a standard USB type A receptacle. This connector will be used when the WF32 has been programmed to operate as a USB embedded host. The USB device is connected either directly to the WF32, or via cable to this connector.

Connector J12, on the bottom right side of the board is the Device/OTG connector. This is a standard USB micro-AB connector. Connect a cable with a micro-A plug (optionally available from Digilent) from this connector to an available USB port on a PC or USB hub for device operation.

The USB specification allows for two types of devices with regard to how they are powered: self-powered devices and bus powered devices. A self-powered device is one that is powered from a separate power supply and does not draw power from the USB bus. A bus powered device is one that draws power from the USB bus and does not have a separate power supply.

The WF32 can be operated as a self-powered device or as a bus powered device from either the USB serial connector (J1) or the USB OTG/device connector (J12). As described in the power supply section above, jumper block (J15) is used to select the power source to be used to power the board.

For operation as a self-powered device, place a shorting block on the EXT position of J15 and connect a suitable external power supply to either J14 or J17.

To operate the WF32 as a bus powered device powered from the USB serial connector (J1), place a shorting block in the UART position of J15. To operate as a bus powered device powered from the OTG/device connector (J12), place a shorting block in the USB position of J15.

Note that there are two completely independent USB interfaces on the WF32 board, and it is possible for the WF32 to appear as two different USB devices at the same time. These two devices can be connected to two

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