ML1400 and Modbus RTU slave over 485

[Jeff23spl]

hello

I'm trying to use the modbus slave configuration out of a ML1400 (1766132bwa)

I have tried the round din8 (CH0) using pin 4RX and 7TX without success

I also tried the ch2 (DB9) but got info about it could only be RS232...

Is there any pinout diagram availaible with the correct 485 info for din8.

I have found some partial info in the plc manual but it talks more about how using a (net aic) in between but still say it's optional???

any more help would be very appreciated

 

[Mickey]

See pdf and doc below.

 

[Ken Roach]

So the MicroLogix 1400 will be a Modbus RTU Slave, is that correct ?

For such a project, I always verify the program configuration first, by using the RS-232 port an a known-good serial cable, with a Modbus simulator.

ModScan32 and the Chipkin Modbus Scanner are my favorites.

On the MicroLogix 1400 Channel 0, pins 1 and 8 are the RS-485 data pins. Pins 7 and 4, which you described using, are RS-232 Transmit and Receive pins.

To use Pins 1 and 8 on the Channel 0 serial port, configure the port for "485 network no handshaking" in the Handshaking setting for the port in RSLogix 500. That setting causes Channel 0 to use the RS-485 pins instead of the RS-232 pins.

To wire Channel 0 to an RS-485 network, I very strongly recommend the 1763-NC01 cable.

 

[Jeff23spl]

thanks Mickey

For the second drawing, is pin #1 on the left when we look at the cable end (Pin side)?

I cut a 1761 cbl where i'm using blue and blck wire for A and B but still no success

 

[Ken Roach]

If the cable was a 1761-CBL-PM02 (the ordinary programming cable for MicroLogix controllers), then pins 1 and 8 are not connected to conductors in the cable.

This is because on MicroLogix 1000, 1200, and 1500 controllers, pins 1 and 8 are +24VDC and DC Common, and are used to power auxiliary devices like the Net-DNI or Net-ENI.

On the MicroLogix 1100 and 1400, this auxiliary power function was replaced with the RS-485 data pins.

I don't know what the color codes are inside that cable... I haven't cut one apart in a long time.

 

[Jeff23spl]

Ok i'm still set on modbus RTU on the programming side and trying to read 485....First bad check!

I'm using modscan32 with a RS232/485 (Siemmens) converter but it could work directly? (I'll give it a try) Serial cable is it straight or null modem?
I also tried with a Modbus RTU driver on an hmi with no more success...

I will use 1763NC01 for the project but for now i try to use 1 end of a cut 1761 CBL(8pin to 8pin). I have buzzed (Multimeter) what i expect to be pin1 and 8 (Black and blue) But could be mirrored

I will do some more tests and get back...

 

[Jeff23spl]

RS232 with a null modem db9 cable works with modscan32 on my laptop configured for Modbus RTU on plc side (Ch2)

 

[Ken Roach]

Okay, so you have proved that the basic setup and your basic testing tool work, at least on RS-232 on Channel 2.

What is the Modbus RTU Master device ? Give as much detail as you can about its interface, configuration, and wiring, as well as details about what you have so far tested.

One other important thing: RS-485 absolutely requires three wires: Data A, Data B, and Data Common. The phrase "two-wire RS-485" is misleading because it describes the contrast to four-wire RS-485, rather than the actual number of conductors.

Many systems use the shield or ground as the Data Common connection, but Channel 0 of the MicroLogix 1400 requires you to connect Pin 2 to the Data Common conductor.

 

[Jeff23spl]

The ML1400 would be slave and i don't have the Scada details but if i can make the din8 works with 485 and Modescan32, it would be good on my side...

I made all the 485 tests with just 2 wires because it was working previously with few Siemens devices on just 2 But maybe the negative power was also the data common connection...
i will look for that common wire. I also get news to receive the specifi ab cable tomorow...

My first simulator is a RS232/485 converter (Siemens PPI) That usually works converting Modbus serial connection to my laptop rs232 com port.
The other device was a Siemens HMI usin a Shneider Modbus RTU communicartion driver connected to the hmi serial port. TP1200 Comfort.

You gave me very good hints thanks

 

[Jeff23spl]

I got the 1763nc01 cable so no more db9 pin out issues
But still could not get any Modbus data out of it

When i set the port on modbus rtu slave i can clearly see no RS485 blinking light on RX/TX leds on my 485 converter. When i switch the port on 485, the lights blinks but Modscan32 didn't recognize data. Is it still a Modbus protocol or an AB 485 protocol when the ch0 (8pins) is set to 485 ?
There is no place to put the refference adresse for Modbus block so is there a way to do Modbus 485 out of a ML1400 or i would absolutely need a 232/485 converter ?

 

[Jeff23spl]

Got IT!!!

Ken i have found the answer on one of your other post on this subject

To get 485 signal we do need to select modbus RTU (slave or master) but select 485 in the handshaking options (I don't know why this setting is there but it works!)
No handshaking(485 network)

 

[Marcosbelgo]

Hello friends,
I would like to know if you got read data from your PLC directly throught the A-B pins 4RX and 7TX CH 0. I dont have the 1763nc01 cables now and need much to do this............
Thanks