I2C interface for Mitsubishi Fxseries?

[alfbillet 0]

Hi all, I want to connect a digital Potentiometer(AD5251) to an FxON or Fx2n PLC. The problem is that the device I have has an I2C serial interface. There are devices available with another type of serial interface called SPI, which again, I cannot find for Mitsubishi PLC's. Is there a commercially available I2C interface for a Mitsubishi FX series PLC? I have to admit I know very little about I2C except that it is used on embedded microcontrollers. thanks, Alf

[panic mode 246]

good luck... I2C is good for only few cm (inches). it is used to connect things on a same PCB. http://www.embedded.com/story/OEG20010718S0073 don't try to mix embeded and plc products. use encoders with plcs.

[Guest Guest_Alf]

Good point. Thank you for the link. I have read the specs and talked to my local Mitsubishi distributer and you are right, I2C and PLC's do not mix easily. I shall look for an alternative hardware solution using conventional, digital inputs and outputs, to realise the digital potentiometer function. thanks again Alf

[panic mode 246]

i just looked up the datasheet for AD5251. it's an interesting product. problem with plcs is that their i/o is simply too slow for this. even standard I2C (ver. 1.0) runs at "slow" up to 100kbps, newer versions go up to 400kbps and 3.4Mbps. in comparison standard plc i/o is good for up to some 0.1kbps. plcs have high speed i/os etc. but they are not suitable for this type of control either. if i recall correctly I2C is supposed to negotiate speed and set it according to slowest device but i think even so this will be rather slow. if you do need I2C device interface, use MCU. you can have MCU communicate with PLC through RS232 for example. but what exactly you are trying to do? there must be simpler solution...