Microcontroller interfacing [closed]

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I'm new to the world of embedded programming and I'm looking for information about interfacing with a microcontroller using I2C, USB, UART, CAN, etc. Does anybody know any good links, books, tutorials, about this subject? Since I´m a real newb on this subject I prefer if it is as basic as possible.

Answer 1

Since you are already a desktop developer, you can probably jump in somewhere in the middle. Download the user manual for the controller you plan to use. Get the example code from the manufacturers etc. sites for one of the simpler peripherals - UART is good.

Get a development board and an Eclipse/Crossworks/whatever development system that supports your board and get something to work - flash LED, UART echo or the like. Don't try to use a multitasker and interrupt driver first off - just poll the UART with as few lines of code as possible. Why - because just getting a development setup to compile, link, download and run one line of code is a considerable exercise in itself, without any complications from complex code. You have your development setup and hardware to debug first before you can effectively write/debug any code for the controller. Just getting 'blinky' code that merely flashes an on-board LED to work is a huge step forwards:)

Most controllers have dedicated groups/blogs, either on the uC manufacturers site or linked from it - join them.

If you want to get into this efficiently, get a board and try to get it to do something - there is no better way. Once you can get a LED to flash or a UART to issue a string of chars, you're off to the races:)

Developing simple 'blinky' or UART-polling functions are not wasted - you can continue to use them later on when you have more complex code. Blinking a LED, (with the delay-loop replaced by an OS sleep), is such a good indicator that the code is sorta running that I've always kept it in on delivered systems. The UART poll is useful too - it will run without any interrupts and so you can call it from the data/prefetch/whatever abort vectors to issue the many 'CRITICAL ERROR - SYSTEM HALTED' messages that you will get during ongoing development:)

Answer 2

Wikipedia really is as good a place to start as any to learn the basics surrounding each of these mechanisms.

Once you've got a grasp, I'd recommend looking at an actual datasheet and user's guide for a microcontroller that has some of these features. For example, this 16-bit PIC has a dedicated UART, I2C and SPI bus. Looking at the relevant sections of the documentation, armed with your new knowledge of the underlying principles, you'll start to see how to design a system that uses them.

The next step would be to buy a development board for such a device and then, using example code (of which there is tons), code yourself up some datalinks. Incidentally, a UART is certainly the easiest to test, since all PCs can transmit using the RS-232 protocol from a terminal, so in this case you can code a loopback to transmit and receive characters with relative ease. With I2C and SPI however, I think you would need to buy a dedicated host dongle to allow you to transmit using the protocols, although I think Windows 8 might be introducing native support (but don't quote me on that).

I haven't implemented a datalink using CAN, so I can't comment specifically, although I just did a quick Google search and there's a PIC family that supports it, so I'm sure you could follow a similar approach. As for USB, I consider it a bit of a black art, so I'll leave someone else to answer that one - although I do know you can get a USB software stack for PICs, so again, a similar approach could probably be followed.

On a final note, I've only mentioned PICs as an example microcontroller. If you're not familiar with microcontrollers in general, you'll soon realise that all the major microcontroller families from companies like Microchip, TI and Atmel generally follow the same design, so I would have a browse and pick the family who's documentation you're most comfortable with (or least uncomfortable with, as suggested by Martin James!).

Answer 3

For the most part the data sheet or reference manual for the microcontroller you intend to use is what you need. Each vendor will implement these interfaces in different ways, so that is your only definitive source for low-level programming information.

I²C and UART are relatively simple with no standard higher-level protocol stack; that would be defined by you or the device you might be connection to. Your microcontroller vendor will almost ceratainly have example code and/or application notes.

CAN is more complex, and typically CAN networks use a higher-level application protocol of which there are several for different application domains such as CANopen, NMEA2000, DeviceNet, IEC J1939 and more. Most often a third-party library is the most cost effective method of implementing an application protocol stack, but if the network comprises of only devices you are implementing, then that complexity may not be necessary. Again your microcontroller vendor is likely to have examples.

USB is very strongly defined by the USB Implementers Forum, and protocol stacks are non-trivial. Most microcontroller vendors that have on-chip USB interfaces will provide sample code and application notes for at least device-class USB. USB Host stacks are more complex, and again the use of a third-party library (which are relatively expensive) is the quickest way to market. Fees you would otherwise be obliged to pay the USB IF may make writing your own host stack no less expensive. Even for a USB Device interface you will strictly need a USB Vendor ID at $2000 from USB IF. Some microcontroller and library vendors will allow you to use their Vendor ID for a defined subset of Product IDs at little or no cost, but you would probably have to be a significant customer in terms of volumes. For internal experimentation, you can probably get away without an official VID, but such a product could not be released commercially.