Hello,

it is required in this case to better describe HW components used, especially type of ET200S (CPU / IM), 1SI module type. It is expected that ET200S system isn't supported with direct connection and library usage in specific modules inter connection (PN/DP/...), only ET200SP I expect. Libraries are created for S7-300/400 CPUs and ET200S HW. In this case (your better description of modules is missing) I recommend maybe solve this with add ET200S CPU to solve this problem, I expect you have IM here not CPU and your MB RTU can work. Other data exchange incase you need them at higher level CPU (1500) you can then pass data via available connection (PN/DP/...) but your better description is required so any one can recommend other solution.