Replicate BUT000 standard fields to KNA1

Hello Experts,

I have created some Z fields in KNA1 using append structure, now this KNA1-Zfield value should be filled from CRM BUT000 standard fields. So I want to know for this do i need to do some coding in CRM or ECC?

Since in CRM we are not creating any Z fields we use the standard BUT000 fields which should map to ECC Z fields.

Do we need to do the below steps in ECC..

1) Create CI_CUST and CI_CUSTX structure in ECC.

2) Then need to create FM but not getting which FM in our case SAMPLE_FCTMODULE_DE_EIOUT OR SAMPLE_PROCESS_CRM0_200 OR SAMPLE_INTERFACE_DE_BALE????

OR in CRM we need to do the logic??

Regards,

Jan.