PIC and USB

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or 18F2550

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USB and PIC tutorial

- Part 1 - How to build a USB device with a PIC 18F4550 or 18F2550 - Part 2 - Application: How to build a USB thermometer

Part 1: How to build a USB

device with a PIC 18F4550 or

18F2550

Overview

PIC 18F4550 and 18F2550 are powerful microcontrollers including a full-speed USB V2.0 compliant interface.

With these MCU it's very easy for the hobbyist to design USB devices with very few components.

In this page, I will describe how to use the CDC firmware from Microchip. It permits to emulate a serial port with a PC running Windows or Linux. It's also very easy to build HID devices.

The 18F4550 experimentation board

Here is a picture of the experimentation board:

The following schematic is very simple, only few components are needed. It's a self powered USB device. Please note I'm using the Olimex tiny-ICSD programmer, if you want to use another PIC ICSP programmer, you should remove D1 and D2 and change the connector

(You can click on the picture to get an high resolution picture)

This device is compatible with the microchip USB bootloader

Please note C5 is 470nF (the datasheet recommend 220nF but more is better) and should be low ESR (for example a multi-layer ceramic). Don't forget the 100nF decoupling caps.

Here is a possible implementation

Click on the picture to get a 300dpi PCB

You can look at the wire's colour of your USB cable: Black=GND, Red=+5V, Green=Data+, White=Data-

The software

You can download MCHPFSUSB_Setup on the Microchip website. It's a windows .exe :(. The firmware we will use is written in C (for the C18 Microchip compiler). This code is (royaltyes) free, but it's not a free software, so it's not possible to redistribute modified source code

In this archive, you will find:

● The USB bootloader and its source code in C18 ● A windows utility for the bootloader ● The CDC firmware source code (serial emulation) in C18. It can be used

with the USB bootloader without modification ● Another firmware for the HID device ● A windows driver for CDC (under linux CDC-ACM is natively supported)

Some tips for your prototypes:

Source code is in the fw/cdc/MCHPUSB.mcw directory

You should comment the following lines in usbcfg.h for a self powered usb device:

#define USE_SELF_POWER_SENSE_IO#define USE_USB_BUS_SENSE_IO

On my schematic, LED's are connected on port B. So you should modify io_cfg.h

#define mLED_1 LATBbits.LATB0#define mLED_2 LATBbits.LATB1#define mLED_3 LATBbits.LATB2#define mLED_4 LATBbits.LATB3

You can put your own code on user.c. For example, look at Exercise_Example() in user.c.

Useful functions are getsUSBUSART() (get data) and putrsUSBUSART() (put data other the serial port)

Don't forget to check mUSBUSARTIsTxTrfReady() before to send data.

They are some examples in the exercise directory. For example, the following program (to put in user.c) toggle the LED number 4 when you press the key "1" in the terminal

They are some examples in the exercice directory. For example, the following program (to put in user.c) toggle the LED number 4 when you press the key "1" in the terminal

void Exercise_03(void){if(getsUSBUSART(input_buffer,1)){if(input_buffer[0] == '1')mLED_4_Toggle(); }

Under windows, you must install the provided driver and you can use the hyperterminal utility (19200bd with a 20MHz crystal). Under linux, check the cdc-acm module, a new device /dev/ttyACM0 should appear.

If you don't want to use the bootloader, you must remove the vector remapping section in main.c and change the linker script (look at important.readme.txt in the sources directory)

Next part -> Application: How to build a USB thermometer

PIC and USB

- French version/Version française

- Forum: Microcontrollers and usb

Electronicfr in english

· Linux on Fujitsu stylistic 1200

· How-to build a webserver for 30Euros with

ENC28J60

· A little autonomous robot

· A new autonomous robot project (V2)

· How-to build an usb device with 18F4550 or

18F2550

. New: Discussion forum

Electronicfr en francais

· Fabriquer un serveur web avec un circuit

ENC28J60

· Un petit robot autonome picbasic 3B

· Un nouveau robot autonome à PIC

· Construire un périphérique USB avec un PIC

18F4550 ou 18F2550

. Nouveau: Forum de discussion

Search:

Web

www.electronicfr.com

USB and PIC tutorial

- Part 1 - How to build a USB device with a PIC 18F4550 or 18F2550 - Part 2 - Application: How to build a USB thermometer

Part 2: How to build a USB thermometer with PIC

18F4550 or 18F2550

Sensor and schematic

We will add a temperature sensor to the circuit described in the first part of this tutorial. You can use the very usual LM35 circuit (Datasheet), or many others circuits like MCP9701, TC1047...

The following schematic show how to plug the sensor on our USB experimentation board:

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The firmware

We will add some code for analog to digital convertion and temperature calculation in the file user.x

//Lets add includes for ADC and strings manipulations#include #include #include //[...]// We will write output data in this stringchar input_buffer[64];// [...]

void Exercise_Example(void){ int temp; // [...] else if(start_up_state == 3) { if(mUSBUSARTIsTxTrfReady()) { //A0 set in input TRISAbits.TRISA0 = 1; memset(output_buffer, '\0', 64); output_buffer[(6*5)] = '\r'; output_buffer[(6*5)+1] = '\n';

OpenADC(ADC_FOSC_8 & ADC_RIGHT_JUST & ADC_0_TAD, ADC_CH0 & ADC_INT_OFF & ADC_VREFPLUS_VDD & ADC_VREFMINUS_VSS, 0b1011); SetChanADC(ADC_CH0); Delay10TCYx( 50 ); ConvertADC(); // Start conversion while( BusyADC() ); // Wait for ADC conversion temp = ReadADC(); // Read result and put in temp CloseADC(); // Disable A/D converter temp=temp/7; //Convert in centigrad degrees

itoa(temp, output_buffer); // Convert to a string mUSBUSARTTxRam((byte*)output_buffer,(6*5)+2); start_up_state=0; } } }//end Exercise_Example

The value in Celsius degree will be sent threw the USB bus when the button on RB4 will be pressed. Under windows, you can use the hyperterminal utility (19200bd with a 20MHz cristal) to see the value. Under linux you can use cat /dev/ttyACM0 .

How to use a 18F2550You can use the source code for 4550 with very few modifications. Just select the appropriate device in the MPLAB configure menu. Change the linker script, and set the configuration bits (like in this picture). Remove any references to port D in io_cfg.h. Here is a picture of a small prototype using PIC 18F2550:

Some links about USB

Making sense of the USB standard (Beyond logic) Understanding USB (usbdeveloper) USB 2.0 Specifications(usb.org) USB 1.1 specifications (pdf file)

Getting help

Ask your question to the electronicfr community http://www.electronicfr.com/forum/phpBB2/viewforum.php?f=1.

Disclaimer

ANY CONTENT ON THIS WEBSITE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.

Next

Soon, you will find a schematic for a USB to serial (RS232) converter.