Cardinal Scale - Grasping at Straws

Hi all,

Working at interfacing a Cardinal Scale with a Phoenix Contact ILC130 PLC via RS-232. We have the scale set to stream it's output and can see this in hyperterminal on a connected laptop.

We have the PLC set to receive data on it's RS-232 port which we can send from hyperterminal on a connected laptop.

Putting the scale with the PLC gives no-joy. All settings are 9600,E,8,1. Cables are 3 wires only: 2,3,5 using null modem is of no use as well.

Now I'm looking to the voltage levels for the RS-232 to see if the scale output is low but able to be handled by the laptop but perhaps too low for the PLC? Had another engineer try to scope the serial lines but he couldn't get a signal.

Am I write in assuming that at 9600 baud, the bit width is about 1/9600 sec or around 100 micro-sec? So if we set the scope for about 200 micro-sec/div and have the trigger and v/div right we should see something when the characters are flowing? I may get time to check this out tomorrow...

Thanks for any ideas to try/think about.

Norm

Hi Norm,


I think using scope is waste of time. If the scale output can be read in hyperterminal, cable is fine. If the Hyperterminal can send to PLC you are - almost fine.
The issue is usually in line termination. Hyperterminal likely fixes output by ensuring CRLF at end of each line. (also show it with CRLF even though it received only CR or LF). If PLC expects CRLF, that would explain the discrepancy.

Thanks for the reply.

I don't believe it is CR/LF related. The function block in the PLC program counts characters as they are typed on the hyperterminal screen. We don't have to wait until the Enter is pressed to see what is in the buffer.

The PLC manufacturer's tech guy will be out Friday but I'm trying to make some headway before that. He says he's interfaced to things like this before and is generally a sharp guy. That's why I'm looking to something as obscure as voltage levels.

I feel like a dinosaur around the company as the young kids don't know 'nuthin 'bout that RS-232 stuff... I threw my 2 ft. x 3 ft. 7 bit ASCII poster at him and made him read the first section of The C Programmer's Guide to Serial Communication for good measure (just kidding but I should have).

The first section of that book would make a great intro published all by itself. I've had some of our people use it to learn quickly.