RS232 display

Hey all!

I have an LED display that failed and I need to replace it. The display gets its information via an RS232 connection to a port on my Siemens PLC.

Can I simply buy the exact same model LED display and replace it or will I need to program the new display w/ an address?

There are only 2 wires being used on the display 9 pin serial connection.

You will need to give the new display a serial address.

Depending on the information received the display may only be reading a numerical value and displaying the corresponding text programmed into it:

0 = Off
1 = Running
2 = Pump 1 MOLR Tripped
3 = Tank 1 Low Level
4 = Tank 1 Overtemp
........... etc.

For this you would need the list of values and the display reading that is associated.

That certainly depends on the display ! What brand and type is it ?

It is likely that baudrate, no of bits, stop bits and parity bit must be configured.

Given that RS-232 is a point-to-point connection, it would be odd to be required to configure an address because 232 just communicates with ”whomever is on the other end”. Maybe it’s really an RS-422 port connection?

It's a display that came with the machine. It's a NEWCAL display. It doesn't send any information back to the PLC like a scale would, just displays the current footage and line speed from the machine.

I bought a replacement from the display manufacturer hoping I could simply swap the unit vs paying a higher price from the OEM. I've had to replace it in the past and the OEM just sent a new one in the mail, so I didn't think any programming was needed.

Maybe the display itself gets programmed to receive the information ahead of time? Sorry...I'm VERY new to RS232 communications...

check with these guys they should have what you need I have used them many times

https://www.vorne.com/index.html

Please state the exact type no. It should be printed somewhere, maybe on a label on the rear.
Without knowing the exact type no, it is pure guesswork.

Read danw's post again .....

RS-232 devices do not have addresses, since their is no need for them to "address" each other. Two devices at each end of one cable can ONLY talk to each other.

But RS-232 isn't the only way to do serial data transfer, and any "multi-drop" network (such as RS-422) definitely would need addresses.

Don't assume that because the devices may have *standard* DB-9 or DB-25 connectors that they are RS-232. Some equipment uses other pins in the connectors to implement connectivity to RS-422 or even RS-485 "networks". In multi-drop networks you MUST have addressing built into the protocol so that one device can talk to any one of the others on the network.

Wiki articles to help you....

RS-232

RS-422 & RS-423

RS-485

Saying only 2 wires are used , I would guess it is RS-485. You will need address for it, as well as need to check the comm parameters(baudrate, parity, etc). Then I guess you have some manual from the manufacturer, if you already bought it, so if you mention the exact model and provide some link to the manual, we could try to find out some details, otherwise we are just guessing.
BTW the site of NEWCAL is not opening from my part of Europe.

mdim said:

Saying only 2 wires are used , I would guess it is RS-485. You will need address for it, as well as need to check the comm parameters(baudrate, parity, etc). Then I guess you have some manual from the manufacturer, if you already bought it, so if you mention the exact model and provide some link to the manual, we could try to find out some details, otherwise we are just guessing.
BTW the site of NEWCAL is not opening from my part of Europe.

Click to expand...

The Siemens PLC is connected to the display with a PPI Multi Master Cable that's converting it to RS232.

When I plug it in the display gives me a generic "HELLO -THANK YOU" that scrolls.

The PPI cable shows the LED solid green for PPI but nothing for TX or RX. I made sure the BUAD rate was set to 9600 (as per the original display and the tag on the new one).

I've gotten a replacement from the OEM before and all I had to do was plug it in and it worked fine.

This one I bought from NEWCAL (the display manufacturer) instead (savings of $500).

I don't know enough about RS232 to know if the display itself gets assigned an address before it's shipped or it gets assigned an address on the PLC.

One concern I have is that I have an issue with the PLC, and if I buy another display (this time from the OEM instead of the display company) it will arrive and have the same problem...

Most of the displays I have worked with have selector switches to setup the COMM's what is the model number of yours, some will do 485/422/232

Was it working then just one day stopped working? also look on the multimaster cable and what is the part number? Do you have MicroWin software to look in the program of the PLC to see if its sending the data?

RS232 can have an address, I used some displays that the data sent was for example 01,2345,5678 CR this was 01= address, 2345 speed, 5678 packs/min
The units had 4 wires 1 = RXD , 2 = Com, 3 = Prog 4 = +V so by touching 3 to 4 for more than 3 seconds it put it into prog mode, then touching it again selected address, Baud etc. (cannot remember exact sequence but did give access to set up) so only two wires were used for comms. This means the software in the display accepted all data but only reacted on the same address (so what is different of 422/485) this does the same it's a misconception that 232 is point to point if only RX is used for multi drop system i.e. one unit sending data and all others receive only, other restraint is distance.
I know most 232 systems do not require addresses but there are a number of manufacturers out there that produce 232 displays with addressing i.e. information boards over production lines that can be fed from one PC/PLC via comms. And as for distance I once went to a production facility where exactly this set up had been installed with 7 displays one for each line showing production data, I guess the total length of cable was in excess of 200 Meters and worked flawlessly .

Distance - I tried using the display just a few feet way just in case it was a cable or distance issue, etc. But it didn't make a difference.

I also tried a new PPI Multi Master cable (I figured that would be the easiest solution/issue) but no dice.

https://photos.app.goo.gl/REQREeN9TvXVRGGs8

https://photos.app.goo.gl/jVGNHNhdKGbVtNsv8

It does give a display of 0=/1=/03 not sure if that means anything or not.

The display is preset to RS232.

My thought on 0=/1/=/03 is that is the firmware revision in the display.

daba said:

Read danw's post again .....

RS-232 devices do not have addresses, since their is no need for them to "address" each other. Two devices at each end of one cable can ONLY talk to each other.

Click to expand...

Not to be a "stickler" but that's not quite true. RS232 is a communications layer and while the original standard was designed for full duplex protocols it didn't stick and there are plenty of protocols that will use RS232 and operate in half duplex. That's really what defines the need for an address is full or half duplex. DF1 is a good example. DF1 full duplex doesn't use an address (even though you can configure one) because there will only be two devices I.E. full duplex. DF1 half duplex does have addresses (associated with the slave nodes) yet it will operate on RS232. Modems are the reason for this. With a multidrop modem (most radio modems will operate in multidrop) you have one master and multiple remotes all using an RS232 interface and because you can have more than one remote connected to the master, the remotes must have an address that gives them a unique identifier.
Having said all of that, if the connection is only via two wires, it's not RS232 but rather probably RS485 or even possibly a proprietary protocol.