Using a USB Flash Drive with an Embedded Host

AN1145 Using a USB Flash Drive with an Embedded Host THE DATA LOGGER APPLICATION Author: Kim Otten Microchip Technology Inc. This application stores two types of data: * Low data rate monitoring. This is done by polling the on-board potentiometer approximately once INTRODUCTION per second. The potentiometer reading and time USB Flash drives are a popular, simple and inexpensive and date stamp of the reading are saved to a file method of moving data from one PC to another. Their on the Flash drive. use in the embedded market has been limited, however, * Higher speed time measurement accuracy. This is due to the requirement that a system must have USB done by reading the temperature sensor every host capability to communicate with a Flash drive. 10 ms. The temperature reading and the count of In the past, this usually meant that the system needed to elapsed milliseconds are saved to a file on the ® be a PC. However, the introduction of Microchip's PIC Flash drive. microcontrollers with USB embedded host capability The application also provides a set of simple means that embedded systems can now take advantage commands to interface to the Flash drive (via a serial of this popular portable media. With the ability to store terminal interface) and directly manipulate files on the data to a USB Flash drive, a PIC microcontroller-based Flash drive. application now has virtually unlimited data storage. This application note demonstrates a data logger appli- Installing the Stack cation that can run on the Explorer 16 Demo Board with The USB data logger application is available as part ofthe USB PICtail™ Plus Daughter Board. It implements a Microchip's complete USB Embedded Host Support file system with a simple, but powerful, set of commands. Package (see Appendix A: "Software Discussed in this Application Note" for more details). To install all A Note About USB Flash Drives the necessary project files on a host PC, download the USB Flash drives come in a wide variety of shapes and installation file from the Microchip web site and run the sizes. Many of the Flash drives, with up to 2 GB of mem- executable installer file. By default, the project and ory, utilize the FAT16 file system and a Small Computer Stack files will be installed in the directory structure System Interface (SCSI) command interface. Microchip shown in Figure 1. Application Note AN1045, "Implementing File I/O Func- tions Using Microchip's Memory Disk Drive File System Library" (DS01045), describes an implementation of this file system. Note: Flash drives with more than 2 GB of mem- ory utilize the FAT32 file system, which is not supported by AN1045.