How to get an Allen-Bradley L16ER to talk to serial device?

[mecstudent]

Hello all,

I am a college student currently working on my senior year engineering capstone project. As part of this project, I have been given an Allen-Bradley L16ER PLC to control everything. One component I am having trouble with is getting the AutomationDirect STP-DRV-4850 stepper motor driver to talk to the PLC. The Allen-Bradley PLC only has ethernet to communicate with devices and the stepper driver only communicates through RS232 or 485 serial. I bought a USR-TCP232-306 ethernet to serial converter in hopes of getting the two to talk to each other but I can't seem to get RSLinx Classic Lite to find the converter since it shows up as a yellow question mark. Can anyone help me either get the converter to work or recommend a better solution to get the PLC and the stepper driver to communicate? I should also mention that I'm working with a limited budget so unfortunately getting the official Allen-Bradley serial expansion card seems to be out of the question.

Thanks everyone!

 

[OkiePC]

The port protocols for the STP-DRV-4850 are going to be an obstacle (SCL, ASCII)

If you really need the two to communicate, look for a protocol converter that can bridge between ethernet and serial like this one from RTA:

435NBX

RTA's 435NBX is an ASCII to Allen-Bradley PLC that easily moves your data. Perfect for barcode readers, weigh scales, displays and more.

www.rtautomation.com

In order to get the one you bought to talk to it, RSLinx would not be involved. You would have to learn how to use raw sockets for communication after first making sure your controller supports that feature. I have no experience with that but I found this thread that might help:

AB Generic string communication

Dear All I have a Laser on my table where I communicate via Putty over Ethernet IP I have setup the Putty with a RAW connection and an IP address. I control the Laser via string commands and everything works great :) Now I would like to move this over in a compactlogix PLC, all my string...

www.plctalk.net

If you just need to control it with the PLC, wire up the requisite command signals between the two per your application needs.

 

[Ken Roach]

Your limited hardware budget is certainly a challenge, but it's probably offset by the fact that your labor is included in the training budget, right ?

First, take a step back and define the problem. The adage "a problem well stated is a problem half solved" applies to most challenges.

Are you going to be controlling the motor controller by sending it "step and direction" pulses ? Or are you planning to send it a target position over serial, and a command to start that move ? Or send it a direction and speed, then send Start and Stop commands ?

USR-TCP232-306 appears to be an inexpensive general-purpose and decently industrialized TCP/IP to Serial server. It took an effort just to track down the probable OEM, a Chinese industrial electronics provider called PUSR.

But it's not equipped with firmware that recognizes the Rockwell "EtherNet/IP" protocol and object model. It can do some Modbus serial-to-TCP conversion, but it's not a ControlLogix-compatible ASCII interface like a 1734-232ASC or a device from Digi, Red Lion, Hilscher, HMS, RTA, or Spectrum Controls.


"Open Socket" communications with the CompactLogix is not for novices. I'm an expert and I avoid it when I can spend some money on a dedicated purpose device instead. But in your case it might be the solution that fits your budget and hardware.

Let's start by defining how much data you have to move, and what protocol or format it's in, and whether it has to be bidirectional or you can just send it out one-way.

 

[Ken Roach]

Backfilling:

Step-and-direction is the usual way to control a stepper motor using a small PLC. But the CompactLogix L16's built-in I/O is not the sort that is configured to send very fast series of pulses that are appropriate for that kind of control, like some small PLCs are (notably MicroLogix 1100/1400 and Micro 820/850/870). It's a great little controller for low-end CompactLogix applications but it's not ideal for fast I/O. AMCI makes stepper control modules specifically for the 1734 POINT I/O platform that the L16/L18 use as their expansion I/O.

Someone on Reddit replying to your post there mentioned the 1734-232ASC or -485ASC, which might be a way to send serial data to the stepper controller. I wouldn't endorse it immediately without looking closely at the serial protocol. As the "ASC" in the part number suggests, those modules are best for sending ASCII string data that has termination characters like carriage returns at the end of the strings. I've painted myself into an application corner with those modules before while trying to send and receive arbitrary length series of hex bytes.

If you're set on using the Ethernet/Serial converter, you're going to have to send data over Ethernet using the "open sockets" technique. Get out Wireshark and RealTerm to start troubleshooting from both ends.

 

[tarik1978]

According to the manual, the stepper motor drive supports both RS232 and RS 485 protocols, the structure of the communication protocol (SCL) is a text of strings followed by carriage return CR .
So I think 1734-232ASC (rs232) or 1735-485 (rs332 & rs485) will do the job.

 

[Ken Roach]

Thanks for that point, Tarik ! I am not familiar with the A-D stepper controllers and their comms protocol.

I have a fresh application on my desk where I was given a surplus 1769-L36ERM, and a surplus 1769-ASCII, and told to make them control a set of existing Parker Compax3 servos with an RS485 serial connection. So this general task is on my mind today !

 

[tarik1978]

According to the manual, the stepper motor drive supports both RS232 and RS 485 protocols, the structure of the communication protocol (SCL) is a text of strings followed by carriage return CR .
So I think 1734-232ASC (rs232) or 1735-485 (rs332 & rs485) will do the job.

I made a typo 1734-485(RS422-RS485)