Interfacing with Society of the Plastic Industry (SPI)

[sns8]

I have a chiller with a SPI (Society of the Plastics Industry) communication port. I am trying to communicate to the chiller through my labview RS 485 program. I understand this protocol is ascii binary, 8 bit no parity. I do have the baud rate and the device address too. However, I've never used ascii before, especially writing information to another machine and reading information from it. I have found ASCII tables with control character. Do I begin with these control characters, ex) (start header, start text), then the device address and baud rate, and then insert commands to retrieve information from the chiller?

Sorry if this is elementary for someone, it's Greek to me.

Thanks!

 

[rberek]

Hi

You may not be getting many hits on your post due to its title. SPI stands for Serial Peripheral Bus, not the Society for the Plastics Industry. SPI is a serial bus protocol, as is RS-485. However RS-485 uses differential signaling and SPI does not. SPI also has no start bits or stop bits. I have never used either the Labview program or RS-485, but it would likely take some work to bridge RS-485 and SPI.

As for the data that needs to be sent to your chiller, you will need to get its data sheet for those details. There are no standard headers, etc in SPI. Each device is different.

r.b.

 

[sns8]

r.b.
Thank you for the advice! I attached an example of what I am talking about. I found this SPI communication protocol is old and unique. The manufacture I bought the chiller from does not have much information on the protocol except baud rates and an address. I did some more researching on other manufactures that also use this SPI and they gave me this attachment, but they told me they are trying to get away from it since the protocol is old. Most documents I found online are mostly dated from the late 1990's... Which I don't understand why the manufactures still make devices with it on. But I will try using serial bus protocol and go from there.

Thank you!

 

[keith1200rs]

This is going to be confusing because any references to SPI are irrelevant in the terms most people on here understand it - your problem is one of RS485 not SPI.

What are you planning to use to communicate to the machine? What software will you use to write the software? What hardware?

Keith

 

[rberek]

Wow. The Society of the Plastics Industries DID invent a protocol for communicating with their equipment... Who would have thought. To bad the document doesn't describe the physical layer much at all.

r.b.

 

[bigdogguru]

I found this SPI communication protocol is old and unique.

Unfortunately the SPI protocol Keith mentioned is an entirely different protocol developed by Motorola/Freescale and commonly used in microcontrollers and other processors.

Serial Peripheral Interface Bus

BigDog

 

[sns8]

Kieth- The hardware I'm using are a RS-485 9 pin cable that connects to my chiller and to a 4 port RS-485 Serial Interface for USB from National Instruments,
https://sine.ni.com/nips/cds/view/p/lang/en/nid/14585

Then the USB connects to my computer. The software I am using is LabView, also from National Instruments.
https://en.wikipedia.org/wiki/LabVIEW

I have a program that reads and writes using RS 485 serial communication in LabView. I am able read a loopback when I test it, but when I connect it to the chiller device, I cannot read anything back, not even an error. I believe the pin layout is correct on the 9 pin cable. I believe the problem is with the code. I am thinking the chiller is not recognizing I am sending it the message. Would this be the problem? If so, how would I say that in the code.

In my mind, which is most likely wrong, for the code I would write to the chiller would be: Start text-device address-baud rate-command-end text-end transmission. Start text, end text, and end transmission are ascii character codes. (I work with power and control systems, so I have never touched ASCII before.)
And the protocol is ASCII binary, the most of the documents I have found have the commands in hex, but it gets converted to binary..
I really appreciate the help, thank you!