[SOLVED] SPI maximum distance at 100kbps

[ashugtiwari]

SPI comm distance

HI All,
What is the maximum distance of communication SPI can support with least speed fo communication with single device. Say the speed is 100kbps. Please reply.

Ashutosh

 

[bobcat1]

Re: SPI comm distance

Hi

Few meter to the most

All the best

Bobi

The microcontroller specialist

 

[ashugtiwari]

Re: SPI comm distance

Thanks bobcat
is there any relation for caculating distance for perticular speed of communication in SPI. what will be the approximate figure for distance of communication in SPI for this speed(100kbps).

 

[FvM]

Re: SPI comm distance

I guess, you're refering to the 3.3 or 5V TTL/CMOS/LVTTL/LVCMOS logic signals of SPI chips. They are basically intended for interchip communication rather than external interfaces. With 100 kbps, external cable length is mainly a question of interference susceptibility, I think. If you intend to pass a standard EMC, e.g. burst test with your design, don't do it.

Another question is to use a different layer 1 for the SPI protocol, e.g. RS422 or LVDS differential signaling. Then it's more suitable for external interfacing. But the amount of individual signals with SPI is unpleasant compared to other interfaces as half- or full-duplex UART.

 

[ashugtiwari]

Re: SPI comm distance

Thanks for reply FvM
the environment hwere I am using this protocol is noiseless, you can consider an open ground. And as I have tested it works pretty well for 10 feet cable, but i don't have any max distance specification for my speed for communication.
The communication is with one environmental sensor for atmospheric temperature.
Well, thanks once again for reply.

 

[FvM]

SPI comm distance

I think, a "noiseless" enviroment only exists in a lab. But taking it as granted, the cable capacitance will basically limit the maximum length. You also may experience signal reflections that cause overshoot and ringing. a SPI slave with fast clock input can possibly count multiple clock edges instead of one.