Reading a SSI RS485 rotary encoder with PXI-8423

[ASMED]

I have a Gurley A19 absolute rotary encoder with a SSI RS485 interface. I am trying to read it with my PXI RT. I am clocking the encoder with a PXI-6713 and am trying to read it with a PXI-8423. I am getting error -1073807253 framing error and error -1073807298. I am not sure if I can read this device with the hardware I have. I haven't been able to find any example code for reading Gurley encoders.

[abalma21]

The Gurley A19 encoder uses an SSI RS422 interface.

You should not be using the PXI-6713 generate the special clock that SSI communication uses. Instead, I would recommend you to use a PXI-8433/2 device and the NI-Serial LabVIEW API.

Regards,

Gustave

[ASMED]

Gustave

I have a PXI-8423/4. My question is what do I use for my clock and how do I write it to my encoder through the 8423.

[abalma21]

Hi,

What kind of connector does the Gurley A19 encoder use? It does not seem to be specified in its datasheet and for what I can see in the Output options, this sensor does not have the standard pinout of RS485/422 devices.

Regards,

Gustave

[ASMED]

Gustave

It is a DB9. My encoder part number A20S18SBRS05SCS18P02EN.

http://www.gurley.com/Encoders/Info/A19.pdf

[abalma21]

Hi,

Have you tried using a SCXI RJ50-to-DB9 cable to connect the Gurley A19 encoder to your PXI-8423/4 and then using one of the LabVIEW examples for Serial hardware from the NI Example Finder?

Regards,

Gustave

[ASMED]

Gustave

That is what I am using an RJ50 to DB9 and I am using the example code. I will post my code for you to look at when I get back to the location where my system is.

[ASMED]

Gustave

I attached my code for you to review.

[abalma21]

Hi,

After searching a little more about the Serial Synchronous Interface (SSI) protocol, I found that even though this protocol is based on RS 422 standards, there are significative differences in how data is transferred between these protocols.

The NI-Serial API only supports RS 232 and RS 422/485 protocols.

The SSI protocol used by the Gurley A19 and A20 encoders is not supported by the NI-Serial API due to the differences not only in how the protocols work but also in the pinouts of the Gurley A19 encoder and the standard RS 422/485 DB9 connectors as shown in the table below.RS 422/485 pinout vs Gurley A19/A20 pinout for DB9 connectors

I found more information about the SSI protocol in this Knowledge Base article. At the end of this article, there is a forum link that proposes to use the LabVIEW FPGA Module and a PXI Digital Reconfigurable I/O Module to build from the scratch the SSI protocol application layer.

Warm regards,

Gustave

[ASMED]

Gustave

Thanks for all your help. I did  get my hands on an FPGA board and I am headed in that direction.