SPI interface for FX3U-14mt?

[k0rtess 0]

Hi all, I want to connect a digital module max6675 with thermocouple to a FX3U-14MT-RS485-RTC PLC. This is PLC from AliExpress *click* The problem is that the device I have has a spi interface.  Is there available to connect SPI interface for a FX3U-14MT-RS485-RTC PLC? I have to admit I know very little about SPI. thanks

[panic mode 246]

Mitsubishi makes expansion module for it (FX3U-4AD-TC-ADP) but not sure if this can work on the clones or how much convincing it would take.

low level interfaces like SPI, I2C etc are used for chip-to-chip communication, this is meant to be interfaced directly to MCU and exchange data serially at high speed.

PLCs are different animal and may not have suitable GPIO exposed... and i see no interface on that board, everything is already conditioned to appear as PLC IO. then there is an issue of a missing driver.

One could still choose to use PLC IO but in general they are operating at different voltage levels so hardware interface adapter (level shifting) is needed. Plus PLC IO are way slower than MCU GPIO.

I have still used this on occasion to interface some industrial controller to otherwise incompatible devices. it can work but it requires one to write own code and as mentioned, this is a crutch and tend to be painfully slow. For temperature this may not be an issue as temperature changes are among the slow processes. Good luck...

 

BTW, there is tons of online resources on SPI, this is one of simple interfaces that can be easily implemented even on platforms that do not include hardware port for it. 

Finally, your version is MT (transistor output) so it is tempting to use them as PTO but the issue is that high speed inputs are simply counting received bits, not storing/shifting the value. In other words - slow it is. 

You just need two outputs and one input. Input is used to read the data from chip. Outputs are used to select chip (also works as reset) and send clock. on every clock sent you need to read the bit. in this case there are only 16 bits to read. if your PLC scan time is 10ms, you can create clock with 20ms period or 50Hz. So theoretically you can read the temperature value in 18*20ms=360ms which is not too bad...