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AC800m RS-232 communication receive problem

Hallo,

i'm having problems receiving data via RS-232. I have connected my AC800M to my PC using RS-232 through COM 3 (there's an RS232 sniffer in between). I can write data on my PLC and the PC will receive it perfectly.

I can't receive data on my PLC from my PC (using Termite to send data), although my RS232 sniffer sees the data (so the data was send).

I'm using the standard SerialCommLib (2.3-1). 9600 baudrate, no parity, 8 bits, 1 stopbit, no flow control. Code i'm using:

(* Connect communication *)

IF NOT RS_232_Connect.Valid THEN
      RS_232_Connect( En_C := En_C, 
                Channel := Channel, 
                Valid => Valid, 
                Error => Error, 
                Status => Status, 
                Id := COM3_Ch_Id );
END_IF;

(* Setup communication *)

RS_232_Setup(  Id := COM3_Ch_Id,
               Req := Valid,
               ChSumType := 0,
               ChSumLength := 0,
               ChSumStart := 0,
               ChSumStop := 0,
               EnLineEditor := false,
               EnEchoChar := false,
               Done => Done,
               Error => Error,
               Status => Status,
               ParError => ParError );

(* Write communication *)

RS_232_Write(  Id := COM3_Ch_Id,
               Req := bSendMsg,
               EndChar := 13,
               Done => Done,
               Error => Error,
               Status => Status,
               Sd := RS232_MSG,
                              ParError => ParError );

(* Read communication *)

RS_232_Read( Id := COM3_Ch_Id, 
             Enable := bListenRS232, 
             MsgLength := 0, 
             EndChar := 13,
             NoOfTrailChar := 0, 
             Error => Error, 
             Status => Status, 
             Rd => IncomingMessage, 
             Ndr => Ndr,
                          ParError => ParError );

Comments (4) New comment

epelt Rank: 1963

Asked 6 months ago

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When you are supposed to receive data to PLC is your PLC in Slave mode or is it in Master mode? To send Modbus RTU data to your PLC with PC then your PLC needs to be in Slave mode. Using Read (MBRead) and Write (MBWrite) function block indicates that your system is in Master mode.

Read function block requests data from the slave. This request you can see with the sniffer, then slave should respond to this request and the data is received.

Comments (12) New comment

by epelt Rank: 1963 on 9/29/2020 6:15:24 AM | Like (0) | Report

It's not a Modbus Protocol, just basic RS-232.

by ak Rank: 173 on 9/29/2020 7:18:51 AM | Like (0) | Report

Ouch, my bad. Is COM3 Rx blinking? Do you get any error messages at the Controller log?
I managed to get the communication between PM864 and AC500 via SerialCommLib to work in only few minutes. I have Message lenght more than zero. If i put it at zero then i get Error and Status -30. I used CCB 6.0.0.3

by epelt Rank: 1963 on 9/30/2020 11:52:08 PM | Like (0) | Report

no problem :)

COM3 Rx is blinking yes, so it gets the message. No error messages in the controller log.

And yes, I think it shouldn't be too hard. I tried increasing the massage length, no success!

Because I can see the message is send on my RS232 sniffer and the Rx light is blinking it's something in my code, but I can't see anything wrong with it.

by epelt Rank: 1963 on 10/1/2020 12:37:02 AM | Like (0) | Report

You can see my code in my first post. Message I send with Termite:

Baud rate 9600
Data bits 8
Stop bits 1
Parity none
Flow control none

All same as my COM3 setting on the AC800m.

Transmitted text: Append CR (end message with 13 ASCII)

by ak Rank: 173 on 10/1/2020 1:26:22 AM | Like (0) | Report

I manage to get it working with the end character 13 with pretty identical code to yours. First i didn't use SerialSetup block and it worked, also when i added SerialSetup it work. I also tested with SerialSetup Req input TRUE all the time as in your code.

Do you get any Error with status to Listen block? I switched end char on sending side to 69 and i see some data and occational Error with status 400 (read over 140 char).

My Connect block Channel is 0.3 and SerialComMLib version 2.3-1.

by epelt Rank: 1963 on 10/1/2020 1:50:03 AM | Like (0) | Report

I tried running the code without SerialSetup, no success.

No error status when using the listen block, status = 1 (pending). What program do you use to send data?

"My Connect block Channel is 0.3 and SerialComMLib version 2.3-1."

same here

by ak Rank: 173 on 10/1/2020 2:05:33 AM | Like (0) | Report

I used AC500 PLC not a pc program. My data was about 10 bytes and no special characters. How fast is your send interval? AC800 is pretty slow and if you send data with high frequency then it might get stuck. I used 1 s interval. It can read faster but not as fast as pc can send data. Also did you start sending messages to AC800 after the PLC have booted properly up (user program is running)?

How about the Ndr output? I guess you have written Send block Req to FALSE when you try to read? Have you tried with Listen block no end character and then give Message lenght? With this you should see at least some data.

by epelt Rank: 1963 on 10/1/2020 3:34:06 AM | Like (0) | Report

Can't control send interval. But i manually send some data once.

Yes, PLC is booted up properly.

Ndr stays low, yes Send block Req is set to FALSE when i read.

"Have you tried with Listen block no end character and then give Message lenght?"

Yes I have tried this, but still no data.
Maybe it's the PC program that just isn't suitable for this PLC, I don't know? Can't test it with something else right now.

by ak Rank: 173 on 10/1/2020 3:52:49 AM | Like (0) | Report

RS232 has separate transmit and receive wires and the signal is detected between signal wire and gnd. Is it possible that your cable is somehow wrong on receive side? On AC800 side do you have factory molded RJ45 or is it self made? I've seen few factory wires where structure has internally collapsed between few connectors.

My cable is an old Ethernet cable where only 3 wires used (Tx, Gnd, Rx).

by epelt Rank: 1963 on 10/1/2020 11:25:39 PM | Like (0) | Report

I'm using a factory RJ45 to 9-pin.

Maybe I could try a selfmade cable

by epelt Rank: 1963 on 10/2/2020 4:53:45 AM | Like (0) | Report

@ak

Problem solved after changing the cable! Code is fine :)

Thanks for all your help !

by ak Rank: 173 on 10/2/2020 10:47:45 AM | Like (0) | Report

Nice, always the one you least expect.

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ak Rank: 173

Answered 6 months ago

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AC800m RS-232 communication receive problem

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