How to use RIO communication between 1756-DH/RiO and 1771-ASB

Hi,I'm trying to migrate only CPU from PLC-5 to CLX and I/O modules are still PLC-5 series.

I think, the migration works is almost done but I have an issue.



Rack addressing method (1771-A4B, Dip SW setting) was 1/2 slot addressing.

I didn't change the rack addressing method.

And there were no any errors in CLX when i finished the migration

1756-DH/RIO module was OK too

But an active LED on 1771-ASB was blinking and I/O cards didn’t work.

So, I checked all settings but nothing was wrong.



Finally, I changed rack addressing method to 1 slot and then the active LED on 1771-ASB is fine and I/O cards are good.



How to use RIO communication between 1756-DH/RIO and 1771-ASB for 1/2 slot addressing type?

It must set 1/2 slot addressing because of field wiring and I/O Modules(1771-IBN,OBN) arrangement.

If I can't use it with 1/2 slot addressing, I should be reinstate the original state of this project

What Series letter (A,B,C,D) is the 1771-ASB Adapter ? Was this same 1771-ASB Adapter used with 1/2 Slot addressing on the previous system, or did you substitute a different Adapter during the upgrade ?

The 1771-ASB Series A and B modules do not support 1/2 slot addressing or 32-bit modules. Series C added that functionality in 1991.

1/2 Slot Addressing should definitely work with a Series C or later Adapter.

What physical size of chassis are you using, and how have you configured it in the 1771-DHRIO scanlist ?

Ken Roach said:

What Series letter (A,B,C,D) is the 1771-ASB Adapter ? Was this same 1771-ASB Adapter used with 1/2 Slot addressing on the previous system, or did you substitute a different Adapter during the upgrade ?

The 1771-ASB Series A and B modules do not support 1/2 slot addressing or 32-bit modules. Series C added that functionality in 1991.

1/2 Slot Addressing should definitely work with a Series C or later Adapter.

What physical size of chassis are you using, and how have you configured it in the 1771-DHRIO scanlist ?

Click to expand...

Thank you for your reply.


*What Series letter (A,B,C,D) is the 1771-ASB Adapter ? Was this same 1771-ASB Adapter used with 1/2 Slot addressing on the previous system, or did you substitute a different Adapter during the upgrade ?

-> The letter is ‘B’and I changed a CPU only.


*The 1771-ASB Series A and B modules do not support 1/2 slot addressing or 32-bit modules. Series C added that functionality in 1991.

-> This is very interesting information.
However, they use 1/2 slot addressing with 1771-ASB Series B
I'd like check 1771-ASB firmware revision, but I can't.
Because the machine now is running to previous system.

*1/2 Slot Addressing should definitely work with a Series C or later Adapter.

-> Actually, I have an 1771-ASB Series E for test.
I already replaced it once from 'B' to 'E' but the Issue is the same.



*What physical size of chassis are you using, and how have you configured it in the 1771-DHRIO scanlist ?

-> previous system info. below;


- 1771-A4B ,16 slot

Two chassis setting by 1/2 slot rack addressing (CLX doesn't have rack addressing setting)


-1771-ASB Series B

I/O Rack No. : 1,2,3,4 and 1C,2C,3C,4C (There are two chassis with complementary I/O setting. CLX doesn't have compelementary setting, so the complementary chassis rack no. is changed to +10)

First I/O Group No. : both chassis are 0


-Logix5 (PLC-5/40E)

Rack size : Full
Baud Rate : 57.6k
Checked Complementary I/O Enabled


-> 1756 DH/RIO setting below;

[0] 1756-L71
+[1] 1756-EN2T
- [2] 1756-DHRIO/D

-CH B, Romote I/O

+B <001 0 1> 1771-ASB RACK_01
+B <002 0 1> 1771-ASB RACK_02
+B <003 0 1> 1771-ASB RACK_03
+B <004 0 1> 1771-ASB RACK_04
+B <011 0 1> 1771-ASB RACK_01C
+B <012 0 1> 1771-ASB RACK_02C
+B <013 0 1> 1771-ASB RACK_03C
+B <014 0 1> 1771-ASB RACK_04C

Cleared the issue!

The reason is 1756-DHRIO scanlist

1771-A4B needs 4 rack configuration even not use all (when set 1/2 rack addressing)

I didn't set up all the racks for the test.

Everything is fine now that we've set it all up.

It was my mistake after all.

Your reply helped me to refresh my head.

Thanks Ken Roach!!

Thank you for the details !

My recollection was incorrect; 1/2 Slot addressing was added in Series B firmware, earlier than the hardware change in Series C.

Complementary addressing is tricky; it's an archaic method left over from the PLC-2's limited memory table. But it looks like you the conversion method correct; the 1756-DHRIO should recognize the Complementary switch on the 1771-ASB as a +10 (Octal) Rack Number setting.

Make absolutely sure you are using the correct DIP switch reference in the 1771-ASB User Manual; there are many similar diagrams that correspond to different Scanner types and different Adapter series.


There ought to be some error messages or codes or indicators in the I/O tree elements in Studio 5000.

Edit: I was pondering the layout when you posted. Yes, this is Four "Full Racks" of memory coming from a single 16-slot physical chassis.