Newbie Question #3 - about the LOR USB-RS485 Communications Adapter

[EdNetman]

Hello,

 

When I purchased my setup I received the basic USB-RS485 (Mini-USB to RJ45) Communications Adapter.

 

http://store.lightorama.com/uscoad.html

 

After looking at the paperwork I noticed that the USB485B has dual RJ45 outputs.  I probably should have upgraded to that one as it would have made life easier last month.

 

My question is simple, can I use a small Netgear switch to run cables in different directions as opposed to daisy chaining them?

 

I have 3 CTP16PC-ReadyToGO controllers and they are spread across 2 acres, so 3 direct runs would be less of a pain.

 

Thanks,

Ed

[PhilMassey]

Absolutely not. LOR protocol is NOT ethernet. and is not compatible with any ethernet components.It just uses CAT 5 cables.

Connecting a LOR box to ethernet risks frying either the controller or the ethernet device or both since power is carried on two of the pins.

E 1.31 (which you do not have) does run on ethernet and similarly cannot be connected to LOR RS 485.

The 485 B is the only approved way of splitting RS 485.

[dgrant]

Phil is correct! Do not ever mix RS485 and TCPIP...you will "FRY" something

[EdNetman]

Sorry guys, I didn't mean to cause confusion here.  There was never any intention of mixing TCP/IP and RS485 on the same wire.

 

I am just talking about packet transport along the cable path.

 

After a little research...

 

http://www.bb-elec.com/Learning-Center/All-White-Papers/Serial/Cable-Selection-for-RS422-and-RS485-Systems.aspx

 

There are many cables available meeting the recommendations of RS-422 and RS-485, made specifically for that application. Another choice is the same cable commonly used in the twisted pair Ethernet cabling. This cable, commonly referred to as Category 5 cable, is defined by the EIA/TIA/ANSI 568 specification. The extremely high volume of Category 5 cable used makes it widely available and very inexpensive, often less than half the price of specialty RS-422/485 cabling. The cable has a maximum capacitance of 17 pF/ft (14.5 pF typical) and characteristic impedance of 100 ohms.

Category 5 cable is available as shielded twisted pair (STP) as well as unshielded twisted pair (UTP) and generally exceeds the recommendations for RS-422 making it an excellent choice for RS-422 and RS-485 systems.

 

and

http://www.bb-elec.com/Learning-Center/All-White-Papers/Serial/Basics-of-the-RS-485-Standard.aspx

 

It looks like using a passive hub should be no big deal as long as the LOR units use half-duplex communication over 2 wires.

 

I think I will bring my USB adapter in to work with me and connect the cable to a Fluke in order to see what we are dealing with.

I really didn't want to have to buy a dedicated RS485 repeater hub for full duplex configurations.

    http://www.rs485.com/pmhubx8.html

[LOR Staff]

You can NOT do this.

 

RS485 is POINT TO POINT.  If you add any kind of splitter or other Y into a line you will cause impedance mismatches and signal reflections.

 

The ONLY way you can split a RS485 network into 2 or more legs is with an active RS485 repeater.

 

You absolutely can NOT use ANY ETHERNET devices.

[Steven]

RS485 is POINT TO POINT.

Technically, it's a multipoint bus with 2 ends, i.e. a single line. Each LOR controller, and the computer, tap onto the bus. A point-to-point bus has only 2 nodes, one on each end.

 

The ONLY way you can split a RS485 network into 2 or more legs is with an active RS485 repeater.

Since the RS485 bus has 2 ends, you can put the computer in the middle of the bus, and run each end as one of 2 legs. This is what the LOR RS-485B interface does with its 2 sockets.

 

I really didn't want to have to buy a dedicated RS485 repeater hub for full duplex configurations.

You can get a less expensive one from LOR: The RS485 Network Repeater. Not only is it less expensive and much smaller than the unit you pointed out, but it doesn't require a separate power supply, as it gets its power through the LOR network from the nearest controller.

 

You absolutely can NOT use ANY ETHERNET devices.

Ethernet uses very small transformers, one of which goes on pair 2 (pins 3 and 6). These are the same pins that LOR uses to supply power, which will destroy the tiny Ethernet transformers. If your display uses both LOR and E.131, make sure to carefully label your cables.