[Moved] maximum distance of SPI and I2C?

Hi,
What is the maximum speed of SPI and I2C?
And how many slaves we can connect with SPI and I2C interface?

Hi,

There is fixed limit. It depends on device count, device types, clock speed.

An IIC is mor simple, only two wires. It is slower than SPI.
An SPI is more flexible, because you may add high speed differential drivers (RS422, LVDS ) for long distance communication.

Klaus

I have seen an I2c link 20m long. With line drivers, sure. So, some limitation can be specified based on 7 bit address - 128 devices. But it is also question about nothing. To many depencies.

if you are over a metre or so look at Canbus, RS485, wireed ethernet, Zigbee, WiFi, etc

Lets say that I2c - is an interface in dimensions of one PCB. SPI can be traced to closest PCBs by sockects and short wires. But also careful. For high speed SPI long wires could cause a problem.

Hi,

my post#2:

There is fixed limit.

Click to expand...

i wanted to say : there is no fixed limit.

sorry for that

Klaus

Is there any reserved address?

What is the maximum speed of SPI and I2C?

Click to expand...

SPI isn't a standard and therefore doesn't dictate any limit for the upper frequency limit. In fact it doesn't even define the medium of transfer so the frequency is dependent on the capabilities of your logic and signal quality.
I2C is a well defined standard. Maintained by NXP (formerly Philips). You can find the maximum ratings in this document:

Of course in some cases you can exceed these ratings without malfunction.

And how many slaves we can connect with SPI and I2C interface?

Click to expand...

Again for SPI the limit is dependent on the capabilities of your logic and signal quality.
With I2C, the absolute upper limit is determined by the width of the address space (7 bits for regular and 11 bits for extended). You may however run into problems with far less than the maximum number of devices and this may force you to either shorten distances or reduce the communication speed if you want to add devices. Lowering the value of your pull-up resistors is also an option.