1791r 8b8p to 1756 DHRIO comm problem

I'm trying to get a 1791r 8b8p to communicate with a 1756 DHRIO card. Both channel A and B on the DHRIO card are set to RIO. I have a 150 ohm resistor on each end of my blue hose. I have double checked that the blue and clear wires are connected correctly (line 1 = blue, line 2 = clear). My 1791r dip switches are set 00011000 for SW1 and 00000100 for SW2. The fault I'm getting is Code 16#0312 Connecting Request Error: Invalid Link Address.

Does anyone have any ideas?

Is that error code on the 1791R entry in the I/O tree, or on the 1756-DHRIO module itself ?

Can you post your *.ACD file or a screenshot of the adapter configuration for the 1791R module ?

I haven't used the 1791R modules personally, but I've used a lot of other RIO devices over the years. The cardinal rule of wiring seems to be "if it doesn't work, swap blue and clear" because so many devices are dual-purpose (DH+ and RIO) and can only be labeled once.

What is the status of the RIO channel LED on the 1756-DHRIO ?

If you were listing the DIP switch values as 1-8 left-to-right, they mean:

SW1 00011000
Starting Quarter 00
Rack address 06

SW2 00000100

Comm Rate 57.6
Output Reset on comm fault
Processor restart automatic
Last I/O Rack
Filter Speed 2 ms


A word about "Last Rack", because this setting can be confusing. It's frequently assumed that this setting indicates that the device is the last device on the daisy chain, or that it is the highest-numbered device on the link.

What it really means is that the adapter is the highest fractional-rack addressed device in its logical chassis.

If you have, for example, three 1203-GD1 devices addressed as:

Rack 02, Group 00, 1/4 Rack
Rack 02, Group 02, 1/4 Rack
Rack 02, Group 04, 1/4 Rack

and there is no Rack 02, Group 06, 1/4 Rack.

That means that the third device (R02/G04) is the "last chassis" in the logical Rack and the scanner does not have to attempt to scan another adapter with the same Rack number.

This is an artifact of the PLC-2 Universal Remote I/O scanner and seldom makes a difference in RIO performance, but I thought I'd mention it here.

fixed

Ken,
Thanks for the response. Turns out the problem was in the dip switch settings. The manual gives various rack numbers based on the dip switches. It all depends on what processor or scanner you are using. Unfortunately, the manual says nothing about contrologix. So I was scanning for the wrong rack.
I hopes this helps anyone else who's using this same equipment.
George