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Old October 29th, 2015, 12:10 PM   #1
splintertje
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Allen bradley communications protocols with RS485

Hello,

I am working on a project, with an allen bradley micrologix 1400 PLC. It has to communicate with a sort of controller which drives a flip dot display.

The project is low on budget and i didn't get much time for the project. But the controller board for the flip dot display, it works whit the protocol RS485. Info off the flip dot display's and controller boards can be found here: http://www.flipdots.com/control-units.html#.VjJPUDZdGHs

I'm using the allen bradley micrologix 1400, and i'm trying to set up a connection for rs485 at channel 2. Because channel 0 is used by an rs232, panelview c200. And channel 1 is for ethernet i think.

I'm programming for some weeks now, using verry diffrend programs and using diffrend function blocks. But i can't get it working. So maybe someone hase a suggestion what i can try? As what I should use for function blocks for instance? Basicly the first question is how did i set up an RS485 connection whit an allen bradley PLC using channel 2? The next question is how can i use the connection to communicate with the controller board?

With kind regards,
Cornι
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Old October 29th, 2015, 01:13 PM   #2
AGill
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I believe that channel 2 is exclusively for RS232. See page 207. And channel 0 could be used for either RS232 or RS485. Perhaps you could move your Panelview connection to channel 2 to free up channel 0 for your flip dot display.
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Old October 29th, 2015, 02:27 PM   #3
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Okay, then i'm gonna try to use channel 0, but is the DH485 the same protocol as the RS485, or did i have to use another protocol?
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Old October 29th, 2015, 02:47 PM   #4
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No DH485 and RS485 are not the same thing. DH485 uses RS485 connectivity but it is its own protocol. You’ll need to use an RS232 to RS485 adaptor. Having said that you need to find out if the display accepts ASCII commands/strings. If so then you should be able to make it work. If not then you are probably out of luck.
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Old October 29th, 2015, 03:07 PM   #5
AGill
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splintertje, I think you'll be fine using RS485 over channel 0. The trick is to knowing the display unit's commands. The flipdot website is somewhat lacking of info.
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Old October 29th, 2015, 03:15 PM   #6
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The FlipDot vendor isn't doing anyone any favors by referring to RS-485 as a "protocol" and linking to Wikipedia.

Nothing on their website describes their "simple command protocol" in any detail.

Step 1 is to switch that HMI over to Channel 2 so that Channel 0 is available for RS-485 connectivity. The 1763-NC01 breakout board is a good way to plug into the RS-485 port, or you can make your own connector.

Channel 0 must be configured for "RS-485 No Handshaking" to enable the RS485 signals on Pin 1 and Pin 8. Otherwise it will use the RS-232 pins for all communication directed toward that port.

Step 2 is to get a description of the wiring and the protocol from the FlipDot vendor.
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Old December 1st, 2015, 02:01 AM   #7
splintertje
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Well i have some documentation from the flipdots vendor.

I have changed the configuration from the channels, the flipdot control board is now connected with channel 0. Using a allen bradley 1763-NC01 cable. But now i have set up the connection to an RS-485 connection, i suppose i use the df1 protocol, but where can i set it is an RS-485 connection and not a RS-232?

According to the manual that is send to me by the vendor:

The display can be controlled In one of the following two modes:

- segment mode – control software is sending information about a state of each segment of a digit. As a
result it is possible to show any combination of segments.

- ASCII mode – control software is sending ASCII characters and some of them are defined in a
memory of a controller (a… f, -, 0… 9, space). If the defined character is being transmitted, it is shown
on the display, if undefined character is transmitted it shown as ‘space’

Segment mode example:
'0' → 0x7E '1' → 0x30 '2' → 0x6D '3' → 0x79 '4' → 0x33 '5' → 0x5B '6' → 0x5F '7' → 0x70 '8' → 0x7F '9' → 0x7B

0xAA Start character
0x55 Mode indicator
0x02 Number of characters -1
0x00 Offset of the first character
0x00 Address of the display
0x30 ‘1’
0x6D ‘2’
0x79 ‘3’
0x16 checksum

Character mode example:
0xAA Start character
0x56 Mode indicator
0x02 Number of characters -1
0x01 Offset of the first character
0x00 Address of the display
0x31 ‘1’
0x32 ‘2’
0x33 ‘3’
0x96 checksum

At this moment i don't know wich data type i have to use. I think i need to use an ASCII data type but i'm not sure about that.
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Old December 1st, 2015, 01:00 PM   #8
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Excellent information !

In RSLogix 500, click on Channel Configuration, then the Channel 0 tab.

Set the "Driver" field for ASCII.

Set the appropriate serial speed and framing. The most common settings are 9600 baud, 8 data bits, no parity, one stop bit. The FlipDot manual should tell you those settings.

Set the Protocol Control -> Control Line selection for "No Handshaking (485 Network)".

That Control Line selection causes the MicroLogix 1400 to use the RS-485 signals on Pins 1 and 8 instead of using the RS-232 signal pins.

Leave all the rest of the settings in that window at their defaults.
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Old December 1st, 2015, 01:19 PM   #9
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I was looking at that checksum and scratching my head.

I think that the checksum uses only the display characters, and does not use the first 5 bytes of the string.

Now we get to roll up our sleeves and work MicroLogix strings.

Let's start with getting that sample message sent correctly.

In RSLogix, you can enter a String with backslashes to indicate that the next two characters are a Hex value. RSLogix will convert some of those to printable characters and some of them to shorthand for control bytes, like "^M" for hexadecimal \0D. This has some historical precedent and can be confusing for novices, but follow along.

You will enter into a String data table element like ST9:0 these characters:

Code:
\AA\56\02\01\00\31\32\33\96
RSLogix will convert that to

Code:
\AAV^B^A\00123\96
You'll need to use the ASCII Write (AWT) instruction to send that string out the serial port of the MicroLogix.
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Old December 1st, 2015, 06:45 PM   #10
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excellent answer
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Old December 1st, 2015, 06:53 PM   #11
Ken Roach
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An example of how the AWT instruction would be used in ladder logic.
Attached Images
File Type: png ASCII_FlipDot1.PNG (26.0 KB, 91 views)
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Old December 1st, 2015, 07:26 PM   #12
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It is pretty easy. Firstly, you should send a example command to the flip dot display by the computer. If you can control the display by the computer then you can control the display by micrologic 1400.
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Old December 8th, 2015, 02:57 AM   #13
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Yes, it works! Thank you for the assistance! The HMI is now programmed over Channel 2, and the flip-dot display over channel 0. The checksum is indeed the sum of the three digits.
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