DH485 and RS485 is the same?

[asteroidehk 1]

Hello friends I am confused. I want to communicate a Micrologix 1100 with a display. I have done this with a ML1500 (COM1=ASCII) a RS232-RS485 converter to the Display. It works fine. Now, I need to do this with a ML1100. According with the ML1100 features: Isolated RS232/RS485 combo port. Also, I am attaching and image with the comms specs. What does it mean? Can I use the minidin port has RS485? How should I connect? In RSLogix Channel configuration should I select DH485 o RTU Master o Slave o what else?? ( I need to read/write from/to display). Somebody has used as RS485 port? Thanks a lot Edited 27 Feb 2015 by asteroidehk

[b_carlton 61]

RS485 is an ELECTRICAL standard for communication. Various protocols can use it. DH485 (unfortunately named nearly the same) is a protocol from Allen Bradley which can be implemented via RS232 (point to point) or via a specialized network which uses an electrical standard similar to RS485 but with additional signals. In typical applications the display is the only unit which starts each communication. If ASCII worked for the 1500 then select ASCII for this application. For ease of connection use the 1763-NC01 breakout for easy access to the RS485 signals. Edited 27 Feb 2015 by b_carlton

[asteroidehk 1]

Thanks for the fast response. I wrote the ML1500 program just for the display. (I am doing trials with ML1500, to incorporate later to another program) Then, using the 1763-NC01 cable in ML1100 COM0=ASCII I could use the same ML1500 program: changing ML1500 to ML1100 processor in controller properties COM1:ASCII to COM0:ASCII the same ascii instructions will work for RS485? Does it mean that the RS232 and RS485 communication is sent through ML1100 COM0 at the same time but for different pins? so, I could eliminate the RS232 to RS485 converter. Thanks again Edited 27 Feb 2015 by asteroidehk

[b_carlton 61]

Yes, the port should be sending to both RS232 and RS485 pins at the same time. The same instructions should work. But as a warning, I've only used the RS485 capability for Modbus, not ASCII but I see no reason why this shouldn't work.

[asteroidehk 1]

:-)Hello I have tried to do this with a ML1400, because is the PLC that I can get for now. I have changed Micrologix 1500 to Micrologix 1400 in controller properties. COM1 to COM0 But, AWT instruction is not writing. According with some info I should change channel mode to user mode, I am trying to do this without result yet. Thanks again.

[JRoss 84]

Can you post your program?

[asteroidehk 1]

Program attached. AWT is not writing. Thanks in advance. ML1400_CHAN0.RSS

[JRoss 84]

Actually, it would be helpful to see the working ML1500 example too, if that's possible. And what is the display?

[asteroidehk 1]

Hello Attached is the ML1500 working program. From this program I changed: ML1500 to ML1400 processor in controller properties CH1 to CH0 Downloaded to a ML1400, but AWT instruction is not working. The display is a production display with RS485 communication, Through Channel1 I am sending 2 bytes and receiving 32 bytes with the actual count. (RS232 to RS485 Converter) With ML1500 the program is working, but now I need to do with a ML1400 and ML1100, this PLC has RS485 Communication in CH0, so I can eliminate the RS232-RS485 Converter. Best regards ML1500_CH1ASCII.RSS

[JRoss 84]

So you're changing the PLC to eliminate the 232/485 converter? My approach would be to get the ML1400 working with the converter, then eliminate the converter. I'm noticing that the communications configuration in the two programs is not identical. Specifically, the Comms Servicing Selection and Messaging Servicing Selection boxes are checked in the ML1400 program and not in the ML1500 program. Also the Protocol Control line is set for No Handshaking (485 Network) in the ML1400 program, but is set for No Handshaking in the ML1500 program. I'm a little shaky with serial protocols (especially given the multitude of variations), so I like to eliminate as many variables as possible when testing.

[asteroidehk 1]

Hello JRoss Thanks for the response. It´s right, I would like to eliminate the RS232/RS485 converter. Not to change the PLC, ML1400 is the PLC that is in the plant. (ML1500 is the PLC that I could get first to do trials). First, I am trying to get the ML1400 working with the converter in CH0:ASCII, but AWT is not writing. I have checked the boxes: Comms and Message Service Selection, also I have checked the handshaking, now are identical, but the problem continues. I have done a test, using CH2 in ML1400, with identical parameters and converter... It´s working¡¡¡, but this channel 2 has not RS485 option, so I can not eliminate RS232/RS485 converter. I am attaching the ML1400 CH2 working file. Why is not working AWT instruction in channel 0? Thanks again ML1400_OK_CH2.RSS Edited 3 Mar 2015 by asteroidehk

[JRoss 84]

Try wiring Channel 0 up for RS232 using the converter. Does that work? My guess is that there is a problem with the way you have the direct RS485 wiring.

[asteroidehk 1]

Hello¡ The program that I attached before is working with CH2 and the converter. (ML1400_OK_CH2.RSS). In this program I have changed CH2 to CH0, using the converter, but AWT instruction never writes. Now I am attaching this new file: ML1400_NOK_CH0.RSS Thanks again. ML1400_NOK_CH0.RSS

[JRoss 84]

So there's a problem with Ch0, whether you are using the converter or not. I've only used Ch0 for ASCII one time, and it worked without a problem. The only difference between my communications setup and the one in the file you attached was that I used a 9600 baud rate where you are using 2400. I also used the AWA instruction, but the only difference between that and the AWT is that it appends the termination characters to the outgoing message. The only thing in the program that looks suspicious is that you are clearing the buffers when the ARL instruction completes, so if the AWT instruction stuck, it might not send. Since the ML1500 program works, and the ML1400 works on Ch2, but not on Ch0, I'm wondering if there's a problem in the wiring. How do you have it wired up? I used a standard Micrologix programming cable when I did my application. Another worse idea is that the Ch0 port is fried. Can you connect to the PLC on Ch0? You'll have to put it back to DF1, of course.

[servando 0]

On 3/3/2015 at 6:35 PM, asteroidehk said:

Hello¡ The program that I attached before is working with CH2 and the converter. (ML1400_OK_CH2.RSS). In this program I have changed CH2 to CH0, using the converter, but AWT instruction never writes. Now I am attaching this new file: ML1400_NOK_CH0.RSS Thanks again. ML1400_NOK_CH0.RSS

On 2/3/2015 at 0:16 AM, asteroidehk said:

Hello JRoss Thanks for the response. It´s right, I would like to eliminate the RS232/RS485 converter. Not to change the PLC, ML1400 is the PLC that is in the plant. (ML1500 is the PLC that I could get first to do trials). First, I am trying to get the ML1400 working with the converter in CH0:ASCII, but AWT is not writing. I have checked the boxes: Comms and Message Service Selection, also I have checked the handshaking, now are identical, but the problem continues. I have done a test, using CH2 in ML1400, with identical parameters and converter... It´s working¡¡¡, but this channel 2 has not RS485 option, so I can not eliminate RS232/RS485 converter. I am attaching the ML1400 CH2 working file. Why is not working AWT instruction in channel 0? Thanks again ML1400_OK_CH2.RSS