Summary of PIC USB HID (Human Interface Device) Interfacing
This article explains interfacing PIC18F2550/4550 microcontrollers with PCs via USB using MikroC Pro. It highlights the critical role of correct microcontroller configuration and USB device descriptors for successful communication. The text details USB speed standards (Low, Full, High, Super) and specifies that Full Speed (12 Mb/s) requires a 48 MHz clock source.Parts used in the PIC Microcontroller USB Interfacing:
- PIC18F2550 microcontroller
- PIC18F4550 microcontroller
- MikroElektronika's MikroC Pro for PIC software
- 48MHz crystal oscillator
Introduction
The purpose of this article is to explain how to interface a PIC microcontroller to a PC via the USB port. Although the concepts are universal, the examples are specifically for use with MikroElektronika’s ‘MikroC Pro for PIC’. PIC18F2550 and PIC18f4550 are famous for their USB Module. To stay ahead you can start with their datasheets.
The most difficult part of this project is exactly what is required to get the PIC microcontroller to communicate with the USB port. The two most important things that absolutely have to be correct are the microcontroller configuration, and the USB device descriptor. If even the smallest thing is incorrect about either of these, communication will not occur.
USB Speed
The original USB 1.0 specification, defined data transfer rate of 1.5 Mbit/s "Low Speed" and 12 Mbit/s "Full Speed". The 12 Mbit/s data rate was intended for higher-speed devices such as disk drives, and the lower 1.5 Mbit/s rate for low data rate devices such as joysticks. The USB 2.0 specification has 480 Mbit/s data transfer rate, which is also known as “High Speed”. The new USB 3.0 specification has up to 5 Gbit/s data transfer rate, known as “Super Speed”.
P18F2550/4550 supports low speed (1.5 Mb/s) and Full Speed (12 Mb/s). So the first thing you have to know is how to set desired clock for USB.
Clock setting
I’ll show you how to configure ‘Full Speed’ i.e. 12 Mb/s. When you use mcu for USB connectivity, it must have either a 6 MHz or 48 MHz clock for USB operation, depending on whether Low-Speed or Full-Speed mode is being used. The first thing you can do is, use a 48MHz crystal (for full speed). But there are two drawbacks:
For more detail: PIC USB HID (Human Interface Device) Interfacing
- What is the primary purpose of this article?
To explain how to interface a PIC microcontroller to a PC via the USB port. - Which microcontrollers are famous for their USB Module?
PIC18F2550 and PIC18f4550 are famous for their USB Module. - What are the two most important things required for USB communication?
The microcontroller configuration and the USB device descriptor must be absolutely correct. - What data transfer rate does USB 2.0 offer?
USB 2.0 has a 480 Mbit/s data transfer rate known as High Speed. - Does P18F2550/4550 support Low Speed mode?
Yes, P18F2550/4550 supports low speed at 1.5 Mb/s. - What clock frequency is needed for Full Speed USB operation?
A 48 MHz clock is required for Full Speed mode which uses 12 Mb/s. - Can you use a 6 MHz clock for Full Speed USB?
No, a 6 MHz clock is only for Low-Speed mode; Full Speed needs 48 MHz. - What software examples are specifically mentioned in the article?
The examples are specifically for use with MikroElektronika's MikroC Pro for PIC.
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Ibrar Ayyub
I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough...