To keep the data up to date change pointers should be configured in transaction SALE, path ALE->Modelling and Implementing Business Processes->Activate Change Pointers for Message Types. That should be followed by scheduling the job for creating IDocs from the change pointers, path ALE->Modelling and Implementing Business Processes->Creating IDocs from Change Pointers->Define Variants and Schedule Job. As these programs run the data will be kept up to date cross system.
CONNECTING SAP PAYROLL AND FI/CO VIA ALE
Part 1: Activities specific to the FI/CO instance
Part 2: Activities specific to the Payroll instance
Part 3: Setting up the RFC connections and logical systems
Part 4: Setting up and distributing the distribution model
Part 5: Testing
Review: Conclusion and more resources