I2C data bus between two instruments?

[drsmith1]

Hi I would like to connection two instrument so that they can communicate with each other. The connection length is 1.5 feet. I will be using I2C protocol.

What precaution should be implemented to address signal integrity and robustness of the communication line?

thanks

 

[FvM]

I2C is typical "inter chip" bus, not designed for usage outside instruments. It will be difficult to achieve industry standard EMC across external cables and connectors.

 

[drsmith1]

I2C is typical "inter chip" bus, not designed for usage outside instruments. It will be difficult to achieve industry standard EMC across external cables and connectors.

my thought was to use shielded twisted pair, do you have any other suggestions

 

[joeyla]

my thought was to use shielded twisted pair, do you have any other suggestions

I would suggesting keeping the clock speed relatively low to begin with a least, maybe 20kHz as you wire capacitance may become an issue. Also pull up reistor should be kept on the low side, maybe ~4.7kohm

 

[FvM]

A twisted pair will bring no advantage for single ended signals. A screened cable is O.K.

1.5 feet isn't a problem as such, you have similar bus lengths inside larger instruments, e.g a TV. It should still work with 100 kHz standard speed.

I forgot that the I2C physical layer is also used as VESA DDC (display data channel) for analog and digital monitors with considerably longer cables.

 

[drsmith1]

I would suggesting keeping the clock speed relatively low to begin with a least, maybe 20kHz as you wire capacitance may become an issue. Also pull up reistor should be kept on the low side, maybe ~4.7kohm

would some type of bus driver have a advantage over a pull up?

 

[FvM]

A regular I2C interface doesn't allow for bus drivesr due to the bidrectional bus nature. Only special I2C repeaters can be used.

The main advantage of I2C is that it supports simple peripherals without an internal clock. It doesn't count when the bus is used between two masters or a master and a second intelligent device like an µP. Serial UART busses will be preferred in this situation.