two peripherals to SLC500 (DH-485 port)

[unsaint33]

Hi, I have 1747-L30A Allen Bradley PLC. It has only one DH-485 port. Whenever I have to connect a laptop to the PLC for troubleshooting, I have to disconnect HMI from it.

Can I connect a HMI and laptop simultaneously to SLC500 (DH-485 port) using a J45 splitter, like the picture shown below?

 

[Ken Roach]

No dont stop please dont unplug now dont stop stop stop

 

[I_Automation]

I feel with you on that, but sorry - Ken's right.


A stamping press I worked on a couple weeks ago has 3 SLC racks in the control panel with a Panelview HMI - all DH-485 with 3 communication adapters. The main rack is a 5/04 and the other 2 racks are both 5/02's. There is no messaging between the racks - all hard wired IO between, all the DH-485 is for the HMI.


To connect to one of the PLC's the cable is unplugged from it and the HMI goes offline whenever it loses 1 of the 3.


EDIT: Same problem working on Mitsubishi's, PC or HMI.



Never saw a DH485 splitter or I would be carrying one around with me.

 

[Ken Roach]

(deep breath)

Ethernet "splitters" are of limited utility even when using Ethernet. When used in pairs (one at either end) they allow you to use a single 8-conductor cable to carry two 4-conductor Fast Ethernet links. They do not function like a 2-port switch or hub.

To plug more than one device into a DH485 port on an SLC-5/0x controller, you properly need an isolator or two. Ideally, two 1747-AIC isolators, or a 1761-NET-AIC isolator/RS-232 converter.

"What would happen if I tried anyway" ?

Neither device would connect to the SLC-5/03 properly.

The DH485 port on the SLC-5/03 controller pinout is:

1 Data B
2 Data A
3 +24V DC
4 Signal Ground
5 Tx-Enable
6 Earth Ground (Shield)
7 Signal Ground
8 +24V DC

An Ethernet Splitter is generally:

Output Pin 1 - Interface 2, Pin 1
Output Pin 2 - Interface 2, Pin 2
Output Pin 3 - Interface 2, Pin 3
Output Pin 4 - Interface 1, Pin 2
Output Pin 5 - Interface 1, Pin 1
Output Pin 6 - Interface 1, Pin 6
Output Pin 7 - Interface 2, Pin 3
Output Pin 8 - Interface 1, Pin 6

A device plugged into interface port 2 of the splitter would get Pins 1 and 2 (Data A and B) connected correctly, but not Pin 4 or Pin 7 (Signal Ground), so it couldn't connect. It would get Pin 3 at +24V, which wouldn't hurt it because it expected that voltage and because it's not connected to Signal Ground.

A device plugged into interface port 1 would get +24V (pin 8) onto what it expected to be Signal Ground (pin 6), and would probably crowbar the SLC-5/03 power supply or smoke the port.

 

[James Mcquade]

what you can do is get a 1747-aic coupler and connect that way.
it will need its own power source. you will also need 1 or 2 cables.
sorry i can't be of much help past that, it's been to long since i did that.
regards,
james

 

[Ken Roach]

I suppose it would be more helpful to post an example of what *will* work rather than what won't.

The way to do this with all legacy DH485 equipment is with two 1747-AIC isolators They have a "trunk" port you connect with a twisted pair (actually 3 conductors), and modular ports for "CPU" and "Peripheral".

You will need some A-B proprietary cables: 1747-C10, -C11, or C20. The only difference is the length.

"Why did A-B use that weird AMP connector as well as RJ45 and have separate peripheral and CPU ports on the 1747-AIC" is a question that was answerable in Cleveland in 1986 but I'm not sure I can address now. The good news is that this sort of cable and equipment is extremely durable and available cheaply on the aftermarket.