Microcontroller programming in C [closed]

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What is the difference between the SPI and I²C protocols, used to program a microcontroller?

Please specify the pins used in each case.

Answer 1

SPI and I²C are bus protocols, and each is well defined:

• http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus
• http://en.wikipedia.org/wiki/I2c

They are very similar in how they work, but they aren't the same and the differences aren't minor.

Depending on the microcontroller, they may have either, both, multiple of each, or none. They may share pins, and they might not. Refer to the datasheet of your microcontroller.

Answer 2

What is the difference between the SPI and I²C protocols

SPI is a 4-wire signalling scheme with a single bus master and several slaves. There's a chip select signal (CS, or slave select SS) dedicated clock signal (SCK) and two data signals, one for reception (MISO = Master In ← Slave Out), one for transmission (MOSI = Master Out → Slave In).

Transmission starts by asserting (= pulling low) SS, then for each bit MISO and MOSI are set after a SCK high→low transition and the actual transfer happens on a SCK low→high transition. Beyond that, there's no such thing as a "standard protocol" carried over SPI beyond the transmission of groups of bits; every component with an SPI interface may define its own.

I²C is a 2-wire signalling scheme, capable of multiple bus masters. It's a lot more complex than SPI, so I suggest you read the Wikipedia article about it.

used to program a microcontroller?

No, because that depends on the microcontroller you're using. Also do you want to write a program for that microcontroller that does communication over SPI or I²C? If this is the case I can give you no answer, because it depends on the controller you're using. It usually boils down to configuring the SPI peripheral (if it got one) or implementing the bit-banging on the GPIOs (which again is specific to the microcontroller used) yourself.

Or do you actually want to program the microcontroller flash over this? If the later is the case take note that the actual programming method depends on the actual microcontroller used and may not happen over SPI at all. And I know of no microcontroller that actually uses I²C for flash programming (except if it has been programmed with a bootloader that does the talking).

SPI is used for programming the Atmel ATMega microcontrollers. But the XMega microcontrollers are programmed using an interface called PDI, which is a completely different beast (uses the reset pin for clock and as a dedicated PDI Data pin).

Most ARM microcontrollers are programmed using JTAG. Then there are interfaces like SWI (which is related to, but not the same as JTAG).

Answer 3

SPI and I²C are defined, see Wikipedia.

Both are master and slave based and can share at least some of the bus. Both are serial based: I²C shares the data line so it is bidirectional, and SPI there is from master and to master. In both cases, these data lines are wired or (you drive zero or let it float and the pull up resistor pulls the line high). I²C is address based, and SPI has separate chip selects for each entity on the bus.

Your question needs work. Some devices can be programmed using SPI, but we generally talk about the microcontroller being the master and using these to program someone else. SPI and I²C busses are standards, but different vendors use them in ways to make it difficult to have a generic hardware interface. SPI more often than I²C will have hardware assist, but it is a good idea to learn to bit bang either and you can always fall back on that.