Mapping more out ports to one out port

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I have a ram memory that consists of several memory units. Each memory unit has, among other ports, data_out port. Memory itself has data_out port and it passes data that comes from one of those memory units. If I try to map several data_out ports of memory units on data_out port of ram memory, an error comes out saying I can't assign more than one value to data_out port. So, how to solve that connecting problem?

Thanks.

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you need to use a switch to get data from relevant block or use rd en if available per block according to overall system read address.