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Application Report

SLAA457A–September 2013–Revised May 2014

Starting a USB Design Using MSP430™ MCUs

Keith Quiring ...................................................................................................... MSP430 Applications

ABSTRACT

This document is a high-level starting point for those wanting to design USB devices with MSP430™

MCUs. It provides an overview of the TI MSP430 hardware and software offerings for USB, as well as

guidance in quickly getting started.

Among the topics covered:

• An overview of the MSP430 hardware USB module

• An introduction to the MSP430 USB Developer's Package

• A hardware reference design for USB devices based on the MSP430 MCU

• A guide to early decisions the developer must make

Contents

1 USB and the Art of Making Something Complex Look Simple ........................................................ 2

2 MSP430 USB Silicon........................................................................................................ 3

3 Software....................................................................................................................... 6

4 MSP430 USB Hardware Design ......................................................................................... 13

5 MSP430 USB Software Design .......................................................................................... 18

6 Getting Started: Evaluating MSP430 USB.............................................................................. 20

7 More Information ........................................................................................................... 24

Appendix A USB Glossary...................................................................................................... 25

List of Figures

1 MSP430 USB Block Diagram .............................................................................................. 4

2 USB System and USB Developers Package Components ............................................................ 7

3 USB Developers Package: Examples from TI ........................................................................... 8

4 MSP430 USB Descriptor Tool............................................................................................ 10

5 USB Host Software ........................................................................................................ 11

6 Java HID Demo App ....................................................................................................... 11

7 MSP430 USB API Documentation ....................................................................................... 12

8 MSP430 Reference Design for USB-Related Pins .................................................................... 14

9 Powering the Entire System From the Internal LDO .................................................................. 15

10 MSP430 USB Clock Connections........................................................................................ 16

11 Example Process for Deciding on a USB Device Class .............................................................. 19

12 MSP430F5529 LaunchPad ............................................................................................... 21

13 MSP430F5529 Experimenter's Board ................................................................................... 22

14 MSP-TS430PN80USB FET Target Board for F552x .................................................................. 23

15 FET Tool (MSP-FET430UIF) Emulator.................................................................................. 23

List of Tables

1 USB-Equipped MSP430 Derivatives ...................................................................................... 3

2 MSP430 Device Test IDs (TIDs)........................................................................................... 5

SLAA457A–September 2013–Revised May 2014 Starting a USB Design Using MSP430™ MCUs

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Summary of content (28 pages)

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Application Report SLAA457A – September 2013 – Revised May 2014 Starting a USB Design Using MSP430™ MCUs Keith Quiring ...................................................................................................... MSP430 Applications ABSTRACT This document is a high-level starting point for those wanting to design USB devices with MSP430™ MCUs. It provides an overview of the TI MSP430 hardware and software offerings for USB, as well as guidance in quickly getting started.
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USB and the Art of Making Something Complex Look Simple 3 4 5 6 www.ti.com .......................................................................... 6 Possible XT2 Clock Sources.............................................................................................. 16 Device Class Tradeoffs .................................................................................................... 18 FET Target Boards for USB-Equipped MSP430 Derivatives .....................................................
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MSP430 USB Silicon www.ti.com 2 MSP430 USB Silicon MSP430 MCUs include an on-chip USB module on several subfamilies. Each family's module is exactly the same, and each is compatible with the MSP430 USB Developers Package (MSP430USBDEVPACK). Although bitbanging USB is possible, it cannot be done at full speed, and it is likely to consume much of the processor's capacity. Most USB applications tend to use the on-chip USB module. 2.
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MSP430 USB Silicon 2.3 www.ti.com MSP430 USB Module Features of the MSP430 USB module are as follows: • Full-speed USB device (12 Mbps). Full-speed is a great match for a 16-bit MCU. It facilitates communication with a USB host, with simplicity and low system cost. The module does not perform low- or high-speed transfers; it also does not function as a USB host controller. • Supports control, interrupt, and bulk transfers. This enables support of the most popular USB device classes.
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MSP430 USB Silicon www.ti.com 2.4 USB Certification of the Silicon To maintain a consistent user experience, it is important that USB devices adhere to compliance standards. Much of this compliance is driven by the USB silicon and software. The MSP430 device derivatives, running the USB API, have passed USB certification testing for all of the device classes that they support. All certification was performed at MCCI, a test house approved by the USB Implementers Forum (USB-IF).
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Software www.ti.com 3 Software 3.1 USB Developers Package: Overview TI provides its MSP430 USB software offering inside the MSP430 USB Developers Package. Table 3. MSP430 USB Developers Package: Contents Item Description Host USB Software Java HID Demo App Host-side example for implementing HID. It complements the HID-Datapipe API, simplifying creation of a general-purpose USB HID device. Python USB Firmware Upgrader Python-based host-side USB firmware update solution.
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Software www.ti.com If your application will only use USB for updating the MSP430 firmware, you can jump to Section 3.6. Most of the software components in the package, about to be described, apply to applications using USB as part of their main function. USB Host: Windows, Linux, Mac, Other Your Host Application x x x x x x x x USB Host Virtual COM Port PC, Mobile, etc.
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Software www.ti.com USB Host: Windows, Linux, Mac, Other HID Demo App (example) HID Demo Guide Virtual COM Port Storage Volume HID Interface MSP430-Based USB Device CDC Interface Mass Storage Interface HID Interface Examples Guide 25+ USB Examples MSP430's USB API Figure 3. USB Developers Package: Examples from TI The red-circled examples help get you started in your development. Each is supported by documentation.
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Software www.ti.com CDC and HID-Datapipe provide the developer a simple data exchange interface. As a brief example of this interface, a simple application follows.
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Software 3.3 www.ti.com MSP430 USB Descriptor Tool TI provides a unique tool for USB development: the MSP430 USB Descriptor Tool. Figure 4. MSP430 USB Descriptor Tool As • • • • • • the name implies, it quickly and automatically generates USB descriptors. This is a big help, because: Writing descriptors can be tedious. Composite devices are far more tedious. Tracking down mistakes can take time. Failure resulting from incorrect descriptors is not always obvious.
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Software www.ti.com 3.4 Host Software, and the Java HID Demo App The kernel-level host drivers for CDC, HID, and MSC are already present within the common host operating systems (Windows™, Mac OS X™, and Linux®). But the developer must identify or create an application on the host that interfaces with the USB device. x x x x User Applications ? x x Host OS x CDC HID MSC Driver Driver Driver x Windows Linux MacOS USB Host PC, Mobile, etc. Figure 5.
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Software 3.5 www.ti.com USB API Programmer's Guide and Examples Guide A complete programmer's guide is included in the developers package to answer your questions. It describes every aspect of writing USB applications with the API. A separate examples guide is provided. The MSP430 USB API Examples Guide is intended for the person only evaluating and running the examples, while the MSP430 USB API Programmer's Guide focuses on development.
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MSP430 USB Hardware Design www.ti.com Because of potential use in the field, the BSL is password-protected to prevent unwanted access to proprietary application software. The BSL must be invoked, meaning that CPU execution must be transferred to it.
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MSP430 USB Hardware Design www.ti.com If internal LDO is enabled (default), VUSB sources out. Can also be sourced in. 3.3V +/-9% VUSB V18 System 220nF >6V 220nF >6V Position caps close to VUSB/V18/VSSU VSSU 5V VBUS VUSB 4.7uF >10V 100, ±5% Supports hardwareinvoked bootstrap loader PUR 1.4k, ±1% 27, ±5% SHIELD VBUS D+ DGND D+ D- 27, ±5% 1M, ±5% IO1 IO2 GND VCC VBUS 10pF >6V, ±10% 10pF >6V, ±10% TPD2E001 ESD Suppressor 0.1uF External clock source >1.
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MSP430 USB Hardware Design www.ti.com The following sections comment on this reference design. They are not intended as a comprehensive guide to good USB design, but rather they address issues specific to MSP430 MCUs. Many good industry resources exist for USB layout and shielding recommendations. 4.2 Selecting a Power Configuration The USB host provides 5-V power over the USB cable, called VBUS. A device can draw some or all of its power from VBUS.
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MSP430 USB Hardware Design www.ti.com For developers who want to source into VUSB from an external source, the Descriptor Tool includes a checkbox for this. If checked, it causes the USB API to keep the internal 3.3-V LDO disabled. However, you must still attach the VBUS signal from the USB cable to the VBUS pin, in the manner shown. The presence of 5 V on VBUS is the way in which USB devices determine whether a host is available; therefore, software needs this signal. 4.
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MSP430 USB Hardware Design www.ti.com If using a crystal, the load capacitors should be properly chosen, according to the crystal's specification. This is especially true if the oscillator will be shut down during USB suspend to save power consumption, in which case improper capacitor selection could result in a slow response to USB resume.
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MSP430 USB Software Design 5 www.ti.com MSP430 USB Software Design Most of the MSP430 USB software documentation is located in the USB API Programmer's Guide, located in the USB Developers Package. Therefore, this section is only an introduction. 5.1 How to Choose a USB Device Class Tradeoffs between the three device classes are shown in Table 5. (Plain text indicates advantages or neutral comments, and italic text indicates possible disadvantages.) Table 5.
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MSP430 USB Software Design www.ti.com Sometimes the choice of device class is clear. In other cases, the application can be considered general purpose, giving the developer options. Although there are many ways to approach this decision, one way is shown in Figure 11. Does the device need to be backwardcompatibility with an existing host PC application? Use the device class for which the original host application was designed.
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MSP430 USB Software Design 5.2 www.ti.com How to Select a Vendor ID (VID) and Product ID (PID) A common question about USB is how to select the VID and PID. 5.2.1 What are the VID and PID? When a USB device is attached to a host, the host asks for its USB descriptors. These tell the host the nature of the device and its capabilities. Included in the descriptors are the 16-bit VID and PID values.
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Getting Started: Evaluating MSP430 USB www.ti.com 6.2 F5529 LaunchPad™ The MSP-EXP430F5529LP LaunchPad (the "F5529 LaunchPad") is a very inexpensive simple evaluation module for the MSP430F5529 USB microcontroller. It is an easy way to start developing on the MSP430 MCU, having on-board emulation for programming and debugging, as well as buttons and LEDs for simple user interface.
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Getting Started: Evaluating MSP430 USB 6.3 www.ti.com MSP430F5529 USB Experimenter's Board The MSP430F5529 USB Experimenter's Board (MSP-EXP430F5529) has more features on a single board than any other MSP430 USB evaluation hardware from TI. It has multiple controls, ports, and power arrangements, allowing a wide variety of applications. Like the F5529 Launchpad, it also has an on-board emulator. Figure 13.
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Getting Started: Evaluating MSP430 USB www.ti.com 6.4 FET Target Boards For every MSP430 device, TI provides simple evaluation boards called "FET target boards". Figure 14. MSP-TS430PN80USB FET Target Board for F552x Table 6.
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More Information www.ti.com FET target boards contain: • A socket for the MSP430 device • The minimum circuitry required for basic operation • Two pushbuttons and an LED • All of the MSP430 pins brought out to headers • A USB connector The FET target boards relevant to USB-equipped derivatives are shown at http://www.ti.com/msp430usb. 7 More Information All of the tools and software described in this document can be found at the MSP430 USB landing page: http://www.ti.com/msp430usb.
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www.ti.com Appendix A USB Glossary 1. Bulk Transfers: One of four data transfer types on the USB bus. Bulk transfers are designed for moving high volumes of data. They are capable of using any free bandwidth on the bus (that is, bandwidth not already used by the other transfer types). This allows them to achieve the highest data rates; but they are given no reserved bandwidth, so on a busy bus, bulk transfers might receive small bandwidth or experience high latency.
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Appendix A www.ti.com 15. USB Device: Also called a USB function. This is a logical or physical entity on the bus that contains one or more USB interfaces. It possesses one upstream-capable USB connector. 16. USB Hub: A device that provides communication between one upstream connector and multiple downstream connectors, allowing more USB devices to be attached to a host. In any given bus configuration, a device is either a host, device, or hub. 17.
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Revision History www.ti.com Revision History Changes from Original (September 2013) to A Revision ............................................................................................... Page • • Added the paragraph that starts "The pullup resistor is specified...".............................................................. 17 Added the paragraph that starts "The diode on VBUS is placed ..." ..............................................................
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