Ascii communications HELP!!

Hello,
I am currently working on a project for the company i work for. I am new to PLC programming and need some help!! desperately!

We are creating a new batching sytem for a manufacturig process. We are using an allen bradley micrologix 1200 and rs logix 500.

The channel configuration is set correct to our knowlege:
Driver-ascii
Baud-9600
parity-none
termination characters-d and ff
no handshaking

Now comes the problem!
We need to get a signal or reading out of a practicon PR444ZV weight contoller using Ascii instruction,Our knowlege of ascii is very limited. we seem to be able to transmit characters, more than just the carriage return, using the ascii write with append (AWA) command. when it comes to undertanding the read (ARD)and clearing buffers ect we seem to be gettin lost. Any basic ascii logic , examples would be marvelous!!
Thanks in advance.

02js4130 said:

Hello,
I am currently working on a project for the company i work for. I am new to PLC programming and need some help!! desperately!

We are creating a new batching sytem for a manufacturig process. We are using an allen bradley micrologix 1200 and rs logix 500.

The channel configuration is set correct to our knowlege:
Driver-ascii
Baud-9600
parity-none
termination characters-d and ff
no handshaking

Now comes the problem!
We need to get a signal or reading out of a practicon PR444ZV weight contoller using Ascii instruction,Our knowlege of ascii is very limited. we seem to be able to transmit characters, more than just the carriage return, using the ascii write with append (AWA) command. when it comes to undertanding the read (ARD)and clearing buffers ect we seem to be gettin lost. Any basic ascii logic , examples would be marvelous!!
Thanks in advance.

Click to expand...

I should probably add that we are looking for two way communication between the plc and pr444zv. our information states that if the host sends "0CR" the pr44 sends "grossweightCR". it is prooving more hassle than anticipated.

It's been a long time ago. It seems to me I had to use the MVM (masked move) to some intermediate N registers and the SWP (swap) instructions to filter out what I didn't need. Sorry I can't be more help, it's been way too many years ago. Maybe someone else has some better ideas. I was reading a scale output and the only way I could clear the scale data was to send two dummy packages across the scales at power up. After that the scale buffers seemed to work correctly.

When I did serial work, I always used HyperTerminal (back when it was a standard Windows accessory utility) to confirm how the device worked. That proved the connection details at the hardware level.

And it showed exactly what was needed in what sequence.

I do recall that even though one could save a Hyperterminal setup, if the setup involved 7 bit ASCII, the saved setup file was not 7 bit, but 8 bit, requiring a manual change to the serial settings.

Check out rtaautomation.com. We use their gateways all the time when dealing with ASCII and they make it very easy.

I second danw's idea about hyperterminal. Testing with a PC is a straightforward way to get started, and to check that your cable is right.

I'll also add that the majority of serial devices I have worked with required a custom cable, so be sure to double check the manuals and the cable you actually built.

DanW has the right idea for a game plan ... basically:

disconnect the PLC and put it aside ...

then use HyperTerminal – and connect a computer to the weight controller ... now determine EXACTLY what text string that you need to MANUALLY type in and send to the weight controller in order to get the desired response back from it ...

get that piece of the puzzle working first ...

once that step has been done, then post a screen shot from the HyperTerminal program – which would show the forum EXACTLY what the weight controller is expecting to HEAR coming in – and an example of what it should SAY back to the PLC ... also give us the ASCII setup information that's being successfully used ...

(syntax and spelling are EVERYTHING in a case like this) ...

with that information in hand, there are probably some folks here who would be able and willing to write the ladder logic code that would meet your needs ...

going further:

I did a quick Google search for the terms "Practicon" and for "PR444ZV" ... nothing popped up that looked promising ... if you can post a link to the weight controller's user manual, then maybe we could offer more detailed help ... (is this a "foreign language" device by chance? – the only link for the PR444ZV search seemed to be written in Italian or something along those lines) ...

If you need Hyper Terminal or a replacement, there are some suggestions here:
http://helpdeskgeek.com/windows-7/windows-7-hyperterminal/

It will really help to have a table of ASCII values. This is one:
http://www.ascii-code.com

Just in the little information you have given there are a lot of possibilities.

You say you have to send d and ff.
Does the d refer to:

• The lower case letter d?
• The ascii control sequence ctrl-d which translates to ASCII code 4 or EOT (End of Transmission) Character?
• Ascii code 0x0d which is the carriage return character?

Likewise, the ff could refer to two lower case 'f' characters but also to the single ascii character 0xff hex (255 decimal).

This is all very doable, but as mentioned, you need to do some detective work before heading into any PLC code.

hello again,

Thank you four your help so far much apreciated!!! i shall try the Hyper Terminal method first and see exactally what need to be sent and received ect.

Here is the link for the practicon unit we are using:
http://www.practicon.co.uk/PR444S-weigh-controller.php

Have a look at this thread:
http://www.automation.siemens.com/W...ow.aspx?PageIndex=1&PostID=508715&Language=en

Check my last post, how I managed to solve the ASCII comunication with a heater.
Hope it helps.