Questions regarding SPI (and I2C)

[Andy Wood]

Hello,

Having never experimented much with SPI (or I2C for that matter), I need to ask a rather basic question - Do SPI and I2C require the use of an accurate (eg. crystal) oscillator, or do they work ok with standard internal oscillators?

What are the pros / cons of SPI vs. I2C?

Regards,

Andy

[Jerson]

Both can work with the standard internal oscillators without any fuss.

I2C is 2 wires, SPI is 4 wire.

[Andy Wood]

Thanks Jerson.

Andy

[Amoque]

I am not very familiar in using SPI, nor I2C for that matter, but as it is on topic and may help both the OP and myself...

Is it correct that I2C must be initiated by the master always, so that the slave device cannot initiate a communication? Say, by example, an I2C clock cannot (by I2C protocol alone) initiate an interrupt (like by the second); rather, must wait for the master unit to read data and determine for itself that the second register is updated? Of course an interrupt line may be used - independent of the protocol - if one is available...

SPI also has this interrupt built into the protocol and one of the required lines may signal that new data is available, yes? Therefore SPI may be more suitable for "active" devices? As our clock example above, the SPI clock (or other SPI device) may signal an updated second register so that the master unit may service this as an interrupt and not bother itself until notified by the slave.

[Jerson]

I2C has 2 variants I2Cmaster and I2Cslave. The master always is in command and the slave responds to the master initiated query/commands.

SPI usually has 4 wires MISO, MOSI, SCLK, CS (Master In Slave Out, Master out slave In, serial clock, chip select). Some devices may signal availability of data on the MISO line when the CS is held inactive. That is implementation specific to that device.

An interrupt line has no relation to the 2 protocols except you might be able to enable / disable the feature via the communications by setting of some register

[Andy Wood]

I have another question - do SPI and I2C (using either software or MSSP) still work ok when interrupts are also in use?

Andy