Are you talking about Safety modules IB8S and OB8S?
It is limited by AENT connections (20).
Each output module uses two connections
Each input module uses one or two connections (configurable)
Another limitation will be 5V bus power and field power
You may need to add EP24 and/or FPD module(s)
Yes i'm talking about Safety modules IB8S and OB8S.
After your answer i have tried to search the information about connections' limit but i can't find them. Also i can't find how to configure IB8S's connections.
Instead I found the informations about bus power and field power.
There are multiple technotes in RA Knowledgebase regarding Point Safety configuration and general FAQs
By default IB8S uses two connections with Output Connection set as "Test Output". You can change it to "None" to reduce connection size to 1.
As a result you will not be able to use Tx outputs as a "Standard Output". All other Tx modes will be OK.
But you have to reserve one connection per adapter for "configuration" and set adapted conenction to NONE (insteead of Rack optimization) if no standard digital modules used.