I have several nodes with Cat3 RJ11 cable in my office. I need to do an I2C communication between several nodes over + 20m and read about the PCA9615 driver. Unfortunately, the Cat3 RJ11 cable has only 4 wires and there is no twisted pair. So do you think I'm going to have a big problem with that? Will EMI noise affect more or less the same the differential (but not twisted) signals?
I need to do an I2C communication between several nodes over + 20m and read about the PCA9615 driver
If you looked at the data sheet for the chip you'll see this diagram: -
The data sheet also says this: -
Construction of the differential transmission line is not device-dependent. PCB traces, open wiring, twisted-pair cables or a combination of these may be used. Twisted-pair cables offer the best performance. A typical twisted-pair transmission line cable has a characteristic impedance of ‘about 100 Ω’ and must be terminated at both ends in 100 Ω to prevent unwanted signal reflections.
And they say this: -
Telecom category 5 (‘CAT 5’) data cable is well suited for this task, but loose wires may also be used, with a reduction in performance.
So, they are not ruling out non-twisted pair when they say this
Twisted-pair cables offer the best performance. However, do yourself a favour and cut out whatever error sources might happen.
Will EMI noise affect more or less the same the differential (but not twisted) signals?
It will produce more noise/interference in non-twisted pair cables.