DH vs DH+


Thread Starter


Nobody ever told me if it's in Blue Hose can it be DH, or DH+, or both... and what are the differences?

karthikeyan santhanam

> Nobody ever told me if it's in Blue Hose can it be DH, or DH+, or both... and what are the differences?

both the DH and DH+ cables are in blue color only. there are function wise difference between DH and DH+. DH+ can support 64 drivers and 64 receiver and to the distance of 10000 feet @56.7kbps(without booster) DH can support 32 drivers and 32 receiver and to the distance of 4000 feet @ 19.2kbps(without booster).

no supporting devices make lots of difference between these two.

DH, Data Highway, was the original communications network protocol that ran on "Blue Hose", a three conductor Belden cable named for its insulator color. Data Highway is used by PLC 2s and 3s primarily. DH+, Data Highway Plus, is the upgraded version that is the standard peer to peer communication today. The PLC 5, SLCs, et al, all have a DH+ port and can be configured for multiple DH+ ports. The only place you will likely see the legacy Data Highway is in a network of older PLCs, usually a set of PLC 2s or PLC 3s wired to a DataHighway to a Pyramid Integrator (PI), which then connects to an ethernet network. In this way, you can have ethernet access to the legacy PLCs going through the PI.

Hope that gives you some more information.


Blue Hose can be DH, DH+ or RIO. Best way to tell is to look at what it is plugged into, and check the part numbers against a catalog.

The difference is basically baud rate, cable length, and number of nodes, IIRC.

RIO is a nightmare waiting to happen.

--Joe Jansen


Ronald Nijssen

<Clip> RIO is a nightmare waiting to happen. <Clip>

Can you explain what you mean with this, I know other (Siemens) systems with similar RIO concepts and wonder if your opinion applies regardless of vendor



Steve Myres, PE

Huh?? I'm interested in hearing what problems you have had with RIO. I've used it quite a bit and it seems very reliable.



My admittedly limited experience with Allen Bradley's Remote I/O system was horrific. DeviceNet is wonderful, but the older style RIO was just too dificult to implement. My worst case was using RIO to connect a SLC 5/04 with 2 panelviews and a FANUC robot controller. Getting the rack/slot configurations set up, and keeping all the M-file data transfers was worse than writing the rest of the app.

Personal experience, and completely anectdotal, but nonetheless, I have never used RIO again. DH+ or DH-485, combined with DeviceNet, can do
everything that RIO can.

--Joe Jansen

I agree that AB RIO is very difficult to program and somewhat limited, but it does work very well after the dust settles.

Bill Sturm


Trevor Ousey

IMO the first time with RIO on an SLC5 is not a nice experience, but using it on the PLC5 is much easier although block transfer seem a little
daunting, things are not bad. As for Devicenet on SLC's, if you need to use explicet messaging, argh...

Trevor Ousey

John Paley--Graphic Pkg Corp


I'm suprised to hear that. I had a plc-2 with two racks of 1771 I/O. I replaced the 2 with a rio adapter and added a SLC5/04 and small rack with a 1746 RI/O scanner and redid the system using the existing I/O. I thought it was pretty darned easy.(albeit all the RIO was discreet--I put the analog stuff in the SLC rack) I configured the scanner in rslogix, and everything was addressed to the scanner slot.word/bit. There were 32 I/O cards so 32 words in the scanner slot. The only potential problem is the difference in the SLC (decimal) and PLC (octal) numbering systems. in the program address I:1.0/8 points to a card point labeled 10. The upper half of all cards bit addresse is offset by 2. This could mean mistakes while troubleshooting.